It happen to e yesterday, i did a factory reset, an boom, it worked great, but u will lose all apps, an unlike the blackberry app store, it wont show u what apps u have downloaded. so My suggestion is, Backup ur contacts with Google Sync, then Do a list of all the Apps u have, and then do factory reset, which is... Application>Setting>Privacy>Reset. its simple
BUT! IMPORTANT. i dont know much about the Android Market(since i bought the phone a week a go), dont know if u payed for apps, u will have to re-buy them or something, so please I SUGGEST! u look for this info before u do anything else!.
BTW, the problem started after i UNINSTALLED a Battery Widget. so yea.