Do you get an error message, or does it just ignore you? If it's the latter, and assuming you're accessing your mail via webmail and a brower, you could try closing out the browser, reopen a new instance of it, and try again. If that fails, try restarting your computer. It's kind of a trite answer, but turning things off and back on can solve a world of problems.
I've been known to slap my computer from time to time, but I can't really recommend that. It sometimes has negative effects.