This all began a month ago with a new build. Components are: Asus Crosshair Formula IV mb AMD thuban 1090T cpu 2 sticks G.Skill 2gb ripjaws xfx ati hd 6950 xfx 850w power supply lancool pc-62 case lg 22x dvd-burner sata wd sata 500gb hd 2 seagate 36gb sata hd soundblaster pci card microsoft keyboard and trackball No major issues while constructing computer. I don't remember any crashes while installing winxp pro. Can't say as to when I noticed the first major lockup. Sometimes when starting computer from cold, it cycles through startup but hangs before completing loading all background programs. These are minimal, just anti-virus program and windows installed programs. I like to have least amount running in background. When this happens I either hold power button to shut down or reset button. This may occur a couple of times before finally completing loadup. Symptoms that occur is that mouse is working, everything else is locked, numlock works on keyboard, Control-Alt-Del does not. I have not overclocked anything on the motherboard, in fact I de-clocked the memory down to 1067mhz. Seems to have better benchmark scores at this setting. You can run benchmarks, play graphics intensive games and never have a problem then go to open a folder or drive, start firefox and have it lock. Sometimes you can leave it for a while and come back to find it locked but I have also left it on all night to find it working fine in the morning. When it is locked it has the same symptoms as bad startup. Have pulled memory sticks and tried single, pulled sound card, seems to be better for a while then reverts to same old problem. Ran memtest and windows memory test suite, does not find any problems, ran these for hours. There is no BSOD and I can't really determine any errors with the event viewer. Have heard that Asus boards are really picky about memory but the ones I have are supposedly supported on their QVL list. Don't see how it could be the PSU, it doesn't drop out when playing games and you would think it would have the biggest draw. Temperatures seem to be fine when entering bios and checking them, no where near there warning limits. Updated bios to latest version. Debating getting new ram but would like exhaust every avenue before that.