Blue Screen

Hello, I keep getting this blue screen:
IRQL_NOT_LESS_OR_EQUAL
It's not my memory, since i have switched memory and it kept coming anyways.
I bought this computer late 2007.
I wonder, What is causing this and how do i fix it?
It usually pops up when i play games or when i watch movies.
Where do i find the crash logs, how do i open them and how do i fix this.

actually can it be my memory voltage or something? when i have about 1 gb ram it didn't crash AS MUCH, but it still happened... I have 1.9 and it is ment to be 1.8. Should i lower/increase it?

Please help me! I also had this blue screen and i can barely play games :/ page_fault_in_nonpaged_area