Check if you have some programs you dont need and unistall them, and also uninstall messenger.
Then download this free program:
http://www.ccleaner.com/
Run all the cleaners there, most important is the registry cleaner.
You might also want to install this free program:
http://www.lavasoftusa.com/products/ad-aware_se_personal.php
And check if you have some spyware messing with your computer.
After those things, install the messenger back.
If those things wont help, also check for viruses.
If nothing works, then your windows may already be so messed up that formatting could be wise.