Hi a customer of ours  has  a Dimension 5150 and the Usb keyboard and mouse have stopped working..they work in BIOS and the NUM Lock light stays on till win XP starts then goes out and the keyboard and mouse don't work.. suspected the usual virus and spyware so removed HDD and scanned with another computer found some and removed them..KB & Mouse still work in BIOS but not in XP.

changed power supply..

checked 5volts at usb ports..ok

updated BIOS from Ver0 to Ver 7..

tried to install XP to brand new hdd,  KB & Mouse worked in BIOS & didn't work in XP....

There's three of us here and were stumped??????