IRQL_NOT_LESS_OR_EQUAL is equally often a simple driver issue.

This error is indeed caused by hardware but also by hardware controllers.
Did you install any drivers just before the problem started?
Did you install anything else for that matter?

Considering the fact your computer is fairly old (average life expectancy of a desktop computer is 3-5 years) it's quite possible you got more severe problems, like the ones stated earlier with your GPU.

Million dollar question: What is the exact errorcode? Eg: 0x000000XX, having this narrows down the searchfield.