Boot problem

Hi guys.
Sometimes at random chances, my Win7 doesn't boot up quite well. Usually, we'd see some sparkles gradually forming windows logo. When it's one of those random events, those sparkles don't show up. And my laptop just hangs up. No activity. None. Zip.
However, when I restart it (after pressing the power button to force shut down -there's no other way) and I choose 'Run Windows normally' the system works just fine...I use the latest updated driver.
Any ideas why?

Maybe it helps: usually it happens after I install/remove some programs. but it's not always the case.

Thanks guys. :)

Hm, have you tried re-installing the operating system?
Doing so will correct any software issue in the computer. Just backup all your documents and re-install.

If that fails, it may be a hardware error.

Test your RAM using memtest86 CD for 5-6 passes or overnight.

Test your HD using maker's full CD diag/repair scan: Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.

Check for a newer BIOS version update on the Support Downloads webpage for your computer or mobo model.

Consider a Repair Install which reinstalls the OS while saving programs, files and settings in place.