Can you uninstall it to an earlier version ?
Yes doesn’t work – deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).
If it is a theme problem I really don’t know what I will do – switching to the Twenty Eleven theme to rule out any theme-specific problems.
I don’t know what this means – resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.