Sleep Issue

I am at my mouse's end ... 1.25 dual, 1 meg ram, leopard, been fighting this for about 9 months, goes to sleep, deep sleep, put a new battery in, zapped the pram, is set to not sleep at all, it ran for 2 months with no problems, walked in and saw the monitor light was "throbbing" knew it was doing it again. I decided to take it to authorized people, they found nothing wrong, said it didn't go to sleep on them, it could be a logic board acting freaky, for $400 I could put one in but it's outdated I should buy a new computer. I picked up my outdated computer and as soon as I plugged it in it started the sleep problem again. Makes me really wonder if they had it plugged in very long. I have moved it to different part of my home, unplugged everything from it, taken it off the battery backup, opened the side up and gave it a blowjob (canned air), ... no difference. Only thing I notice is ichat will go offline and in about 30 seconds the computer goes to sleep. Any suggestions will be appreciated.
last night I put the Leopard disk in and restarted off it ... been running all night long ... I did an archive and install of leopard about 2 months ago .... I am out of ideas of things to do.

Try reseting the PMU.

been there, done that .... it's been running fine since yesterday at 11 am ....