I've been employed to fix a friend's PC troubles and apparently his monitor automatically goes into "sleep" mode whenever the CPU is turned on. Once it passes the initial loading stage (Where the "DELL" screen shows up and the loading bar fills) it goes into sleep mode.

I've tried removing the battery and waiting five minutes (I've removed the battery again and am currently waiting fifteen minutes) but that doesn't help. He's given me the go ahead to wipe the PC itself and I've put the CD in, it boots up from the CD but as soon as Windows begins copying files (the initial stage after it checks system configuration) it goes into Sleep Mode again.

What else can I do to fix this issue?

EDIT: I guess the first time around the CMOS battery hadn't been pressed in all the way or something, as the monitor is working just fine now.