My imac has started to crash recently with "You need to restart your computer. Hold the Power button for several seconds or press the Restart button." Known as the grey screen/black screen curtain. To troubleshoot problem I ran the Apple Hardware Test and received error message 4MEM/1/40000000:0xb951c818. I understand it is a memory/ram problem. My setup is 24" imac 2.93ghz Intel Duo CPU 4GB memory OS X 10.6.4 Anyway to fix this problem, my warranty is out. I would appreciate any suggestions to this problem. Thank you.