Just two days ago, I noticed a problem that's been affecting my gaming performance lately. For some reason, my computer won't put more than around 2,75gb of ram in use - even when my computer needs it. When I'm playing any game, it stutters horribly and I get fps drops every quarter second or something. Heavy games that need memory become nearly unplayable, and light games like Insurgency become hell - though still playable at times, one explosion and my performance dips.

I've system-restored to the earliest point available (which is three days before) but the problem still affects me. I'm starting to wonder if this is a ram problem? I ran four passes on memtest86x and no errors occur (still don't have time to do eight consecutive passes) - trying out memtest64 freezes my computer, though, so there's definitely a problem.

Does anyone know the source of the problem, and perhaps a solution?

One final point - if I don't clear standby memory with RAMMAP then it takes up around 2800mb worth of ram. The rest of the available memory is either used or free. Standby memory doesn't increase past that point - and when there is no free memory the system will not turn standby into in-use.
Instead, when standby memory is cleared, the in-use RAM caps out at around 2,75gb and will not use the remaining free memory.