Ashy

Hey. I've had quite a bit of trouble with this PC in the past. I've had to pull 1gb out of my 3gb of RAM after I kept getting boot errors and other related issues which pointed to either that or my HDD dying. I replaced both in turn which seemed to sort things out. Here I am now, out of nowhere, I'm getting unusual things happen to me. It started yesterday. Out of nowhere, Firefox crashed (as it does) but everything else went too. Windows Explorer crashed and froze, Windows Live Messenger, everything. I had to manually reboot. It happened again another hour or so later, and then I woke up to the same issue. I've scanned a bit of my PC with NOD32 and Windows Live Essentials initial scan, and got back an all clear on both accounts. I've scanned fully with MalwareBytes and it picked up nothing, too. I'm not sure what else to do. I'm thinking it's my RAM, but I'm clueless, as the freezing seems like malware... Any help or diagnosis would be of great help, thanks.