Don't believe the picture opposite for a second. He may look like his privates have just been hooked into the national grid, but Jack Black is generally about as energetic as a sloth on Mogadon when we meet. Only when the camera appears does the voltage soar.

Energy, of course, is what we expect from Black: the scattergun mania and cavalcade of cartoon expressions that shunted him to the front of the comedy queue in such films as High Fidelity, School of Rock and Nacho Libre, and in his parallel career with his satirical rock band Tenacious D.

He is in full fizzy flow again in Be Kind Rewind, the latest film from the frazzled French visionary Michel Gondry, as a man who becomes magnetised (don't ask) and wipes all of the videos in a store minded by his friend (Mos Def). Faced with livid customers and an imminently returning proprietor, the pair set about recreating the films with a camcorder and a backyard full of junk. Among their DIY masterpieces are Ghostbusters and Rush Hour - Black's jerky cardboard re-creation of Robocop is a particular triumph.

But all he is offering today are yawns and half-finished sentences, his languid mood emphasised by his new hair-do, bleached to a stoner-surfer blond for his role in Ben Stiller's new film Tropic Thunder.

That I might not have his full attention becomes apparent when I ask whether he was familiar with Michel Gondry's creatively bonkers CV before he did the film. “Yeah, I'd heard his music,” he drawls. Does he mean Gondry's music videos for artists such as Björk and Aphex Twin? “No, his music.” I didn't realise that he made music, I say. “Yeah, he's done some albums and I saw him act in a couple of things. He's more a jazzy dude than a rappy dude. Hang on - we are talking about Mos Def, aren't we?”

Black could just be jet-lagged, of course. But it's more likely that he's just not very engaged. “I guess I do have a tendency to get bored,” he admits. “If something feels like school I always fall to sleep. I always fell asleep in class, and if I'm in a movie that feels preachy or educational, I'll just doze off.” He yawns expansively.

When something piques Black's interest, though, his enthusiasm is boundless. Mention music, movies or, for example, his membership of the Frat Pack - the loose conglomeration of comic actors that also includes Stiller, Vince Vaughan, Owen Wilson and Will Ferrell - and his face contorts into a loopy grin. “I love it! All of them I think would like to destroy that thing, but I love it. I think those guys are great and I'm in there? Yeah! I'm the only card-carrying member that actually shows up for Frat Pack meetings!” he sniggers.

Black is often at his best when he can keep his powder dry for key moments. Recall the juggernaut vim with which he stole High Fidelity, in which his snooty record shop assistant had only a handful of scenes. “It's pretty fun to have roles where you have to focus hard for limited amounts of time. You can make sure that everything you do has got some funny spice on it.”

His more recent leading roles - School of Rock, The Holiday, Be Kind Rewind - were harder work. “It's more of a marathon,” he says. “If you try to squeeze out a thing so every moment is filled with comedic merriment, that actually gets tired. You don't want the audience to get annoyed with your facial gymnastics.”

Not resembling the archetypal Hollywood leading man has helped rather than hindered him, he insists, “Because in LA the matinee idol looks are a dime a dozen. People who look a little off are more memorable.”

The suspicion remains that Black has been “a little off” for much of his life. Born in Hermosa Beach, California, to two satellite engineers - his mother worked on the Hubble space telescope - he insists that he did not inherit any of their brainpower, only “an interest in sci-fi”. He is Jewish, but not practising: “Part of the bar mitzvah is that you become a man supposedly at 13 years old, and as I was a man I decided never to go to a synagogue again.” The problems started when his parents took him out of his local high school.

“I'd made out with this girl who was going out with this motorcycle gang guy. He beat me up - not too badly, but he wasn't done. He was coming for more - ha ha! I was doing a lot of drugs and stuff in high school and my parents said, ‘Enough is enough, we're getting you out here.' So they put me in this school for [adopts right-on Californian tone] troubled youths.” Would he describe himself as troubled at that point? He nods: “I was definitely in a rut, a bad way.” He remembers his new environment, the Poseidon School, as “intense” - suddenly, he was among 20 other disturbed kids, most of whom had been thrown out of their respective schools. But he flourished, following his “Poseidon Adventure” with a stint at the liberal Crossroads School, where he excelled at drama, and going on to UCLA, before dropping out in his second year to become an actor.

It was at this stage that Black's interest in music became crucial. “I don't think I'd have an acting career if it wasn't for the music, and vice versa. That was my way in, doing both. Music is my jab and acting is my punch, or the other way round.”

His big break (or “first big gig” as he puts it, perhaps tellingly), was appearing in Bob Roberts, as the guitar-playing fan of the titular folk singer-cum-activist, played by Tim Robbins, whom he knew from his involvement with the latter's Actors' Gang Theatre group.

Since then he has appeared in a string of music-related films, from High Fidelity to School of Rock, in which he played a down-at-heel heavy metaller who tutors a class of kids. Then, of course, there's Tenacious D, the absurdist sketch band he formed in the late 1990s with his friend and fellow comedian/ musician Kyle Gass, which found its way on to the big screen in Tenacious D in the Pick of Destiny in 2006.

Black now even has a musical wife, the cellist Tanya Haden, whom he originally met at Crossroads. Their son, Samuel, was born in 2006 and Haden is currently expecting a second child.

He has calmed down, he insists, since his partying days, but his passion for music and movies remains undiminished. There still seems to be much of the fan in him. Does the YouTube-inspired ethos of Be Kind Rewind, in which an average Joe can shoot, direct and star in his favourite movie, strike a chord? “I definitely have my psycho fan side,” he agrees. “Like anyone, I've been reduced to a trembling idiot around people I really admire.”

As a teenager, Black saw John Malkovich in a play, and, afterwards, waited outside the stage door to shake his hand. “I could tell that he didn't really want to do it. I don't blame him, because now I've been through it, when you want to disappear, you've shaken so many hands and signed so many autographs.” The same thing happened when he met Thom Yorke of Radiohead, whom he describes as a god. “He was not into it. All my heroes: not into it when I approach them! What do you hope to get from it? What you hope, even if you don't admit it, is that they will like you and want to be your friend. Which is totally unrealistic and not fair to them. Just leave them alone! Because you're going to enjoy them the same amount from over here, where you never meet them.”

By that rationale, I point out, I shouldn't even be here. “Yeah!” he smiles, animated once more. “Get outta here!”

Be Kind Rewind is on general release from Friday

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