Dell Dimension E521 Problem

Hello everyone. About a year ago I sold my old Dell Dimension E521 to my friend. I had modified it to use an AMD Athlon 64 X2 6000+ (within the thermal and power specs for the system), 3GB of RAM, and a Radeon HD4670 1GB video card. He used the system to play GTA IV and it worked fine up until about 2 weeks ago. We had cleaned it out and put on a new layer of Arctic Silver 5. When we turned the system back on, the system powered up and the main fan started spinning at full speed. Nothing came up on the monitor then suddenly the video card fan started spinning up to 100% then down to nothing then back to 100% continuously. The system diagnostic lights also showed the error code 1 and 3 which means a memory module error. We checked the memory in another system and it worked. Any ideas as to what might be wrong?