She’s sung that she’s not a girl, not yet a woman. And after her performance at MTV’s Video… She’s sung that she’s not a girl, not yet a woman. And after her performance at MTV’s Video Music Awards, I’m not quite sure she’s a talent either.

Possibly the most talked-about thing Britney Spears has done since she shaved her head last spring, her hyped-to-the-point-of-implosion comeback on MTV’s annual award show might be the nail in her platinum coffin. Spears opened the show, which aired live on Sunday, with her new single, “Gimme More.”

For those of you who didn’t watch it Sunday and still haven’t checked it out online, here’s the bottom line: Ms. Spears looked more disoriented than a drunk freshman trying to find the corner of Forbes and Fifth. Her dance moves were executed with the energy of a napping, elderly woman, her vocals were as painfully lip-synched as Ashlee Simpson’s and, well, she just looked as if she’d rather have been at the bar ordering that 17th shot of tequila than anywhere near that stage.

Now, I know that Britney has been through a lot in the past few years – she has given birth to two children, married and divorced Kevin Federline and struggled with a career-damaging substance abuse problem that landed her in rehab. Add in the daunting stress of keeping up appearances, as well as maintaining her musical legacy, and you’ve got the contents of a pressure cooker ready to blow.

Still, wasn’t this supposed to be her comeback? Sunday’s performance could have been her opportunity to put the unforgiving press to rest with a show that proved she still had it – “it” being any combination of her dance moves, looks, vocal talent and stylized lack of clothing. But how could she have hoped to overcome the performer she used to be before she took that nose-dive off the deep end a few years ago?

Herein lies the secret of the comeback, and the reason why it’s time to stick a fork in Britney because boy, she is done.

The musical comeback is a tricky thing and rarely successful. For the purpose of this column, let us define a comeback as such: the act of an artist who, after time away from the spotlight due to lack of relevancy or a self-imposed break, returns to the scene, often unexpectedly. Since the nature of a comeback requires the artist to have spent time away, fans are left with a back catalog of music. With nothing new released, fans have time to ruminate on the artist’s past music, allowing it to solidify as representative of that artist.

Because of this, for a comeback to be successful, it must overcome the shadow of the artist’s past music. For example, if a band releases a huge debut album, retreats from the world for a few years, then puts out a new albumwhich no one but the drummer’s mom really listens to, this band has not experienced a successful comeback.

The tricky part is this: Musicians grow as time goes by. There’s no way that a band can release the same album twice and get away with it, unless, of course, that band is Nickelback. But that is another argument for another column. So, when the new music of the comeback hits, it will most likely be an aural shock for listeners at first. For a comeback to be successful, then, the new music must be of the same quality or better than the old stuff, allowing fans to slowly grow accustomed to the new sound instead of casting off the current music in favor of old favorites.

Now, not every album a band releases must be stellar – most bands encounter a few roadblocks in their careers. The above rule applies most in the case of a comeback, where the band’s whole success depends on this new music, as it can make or break their reincarnation. Similarly, band reunion comebacks do not count in this rule, as no new music is released, and the band is simply playing their old music to new fans.

Let’s use Bon Jovi as an example. In the 1980’s, these Jersey dudes made arena rock anthems like “Livin’ on a Prayer.” When they came back in 2000, after five years off, their music had noticeably changed – from the hair metal of their heyday to soccer-mom-rock, but it still had the same pop sensibilities and catchy hooks. The music grew up along with the fan base, making for a comeback success.

Other success stories include Kylie Minogue, who sang that cheesy ’80s version of “Locomotion,” then came back with the sexy “Can’t Get You Out of My Head,” and Mariah Carey, who went insane for a few years (remember “Glitter”?) and then bounced back with the mega-hit The Emancipation of Mimi. Even Christina Aguilera capitalized on the comeback. After her foray into being ‘dirrty,’ she returned with arguably her strongest, most unique album, Back to Basics.

On the other side of the comeback spectrum, we’ve got Britney. Poor, poor Britney. According to the above logic, it should be no surprise that her comeback will, and has already, begun to flop – before her new album even drops, no less. The new song surely doesn’t stack up with her best (“Toxic”), and her most general entertainment factor has dropped. Even she looked bored Sunday night.

Still, Britney’s not totally cooked. My whole argument may be flawed, and her new album could be absolutely fantastic, a Dark Side of the Moon or Nevermind for the iPod generation. But if I’m right, and the new stuff doesn’t nearly stack up to the old, then she will have some new friends in the busted comeback club. Britney, meet Vanilla Ice.