When my PC gets charged alot it CRASHES

When my PC works really hard, for example I have internet running and MW2 or several youtube videos it sometimes either freezes or a Bluescreen appears saying almost always either "IRQL_NOT_LESS_OR_EQUAL" or "Kernel_Mode_Exception_Handled".
The numbers etc. after that are always different...

I have a strong PC, but only 1GB RAM and a programm that tells me how hard my PC works says when I start Bioshock 2: CPU: 100% (Full Power), RAM: 85% (High Power).
Might it be because some drivers ain´t up to date? When I ask Windows 7 for updates it says everything is fine...How can I check if my drivers are all up-to-date??
PS: Once again: As far as I know this only happens when the PC gets charged alot...

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