start menu auto close too quickly

When i open the start menu it automaticly closes after 2/3 seconds if i dont click in anything.
This is really annoying. I don´t think i have this problem before.

What can i do?

It sounds like your user profile is corrupted. Take a look at this:
Fix a corrupted user profile
I think it should help!

In certain instances I go straight to suggesting the System File Checker

http://www.sevenforums.com/tutorials/1538-sfc-scannow-command-system-file-checker.html

If you have another user on your PC (if not, you can create one to test), see if this issue exists there. If not you might have a corrupted user profile. If you do, this method should work for you.

Fix a corrupted user profile

A Guy