Running out of memory and hard lock (no BSOD)

(first post!) Hello, new here! So I have had Windows 7 Ultimate x64 installed for about 2 weeks now and it has been running great. Games have been running fairly well even with my mediocre video card set up. I understand that with x64 that it's suggested that you run 4 gigs of ram and I am only running 2 gigs (temporarily). I have had no memory problems up until today. For some reason I am totally running out of free memory and my memory usage is sitting around 60-66% as opposed to the 35-40% that its been sitting at for the last 2 weeks. Also i have noticed a spike in my cpu usage and temperature even while there are no "active" programs running. It was around 9-15% and it now stays around 30-45%. After about 20 mins of use, the rig will totally use up all of the memory and hard lock, causing me to have to hit the reset button. No BSOD, just freezed right where it's at. According to task manager and resource monitor there should be no reason for these spikes in my cpu and memory usages. I am currently about to run a serious of malware and virus scans but was looking for some other suggestions. Any help is greatly appreciated!

Run a full anti virus scan
Download and run malwarbytes. Make a full scan after updating ( I see that you have these steps covere)
Download memtest86 and test RAM
www.sevenforums.com/tutorials/105647-ram-test-memtest86.html
Type process explorer in search to determing what is using ram

Cool, ill do the memtest and check out my ram. Ive been all around the process explorer and performance/resource monitor and cannot find anything thats eating up all of this cpu and ram though.

Memtest is good but it takes time. Run for at least 8 passes. If errors are found test each slot with a good ram for 8 passes. If no errors check each slot for 4 passes.

Memtest fine, no viruses or malware. I did however notice that the wmpnetwork was soaking up a ton of memory so i axed it. Its a little better, but nothing like it was. Im thinking about doing a fresh install just for the hell of it.

Try a clean boot, you may get some answers,
http://support.microsoft.com/kb/929135