i'm new to forum. thanks for any help. computer is 4 yr old compaq presarrio. started loosing time about 1 yr ago..didn't know to change battery...9 mos ago started having boot problems..had to TURN on and off several times to GET it to boot..rescently updated windows xp, went to reboot and will not boot. KEYBOARD light up for a split second, hard drive hums and feels like it is spinning. monitor says no signal and nothing harrens...replaced cmos battery, still no boot. have tried every key and combination to get into cmos/bios. no luck. need help please!!
thanksBorrow a power supply of the same wattage or greater and swap it in there and run things overnight...if everything seems OK you need a new PSU...
Don't buy a 20 dollar special or you'll soon be in the same boat.
You can also try another CMOS battery...i have had them DOA brand new CAUSE they sit on the store shelf for years sometimes...A general rule of thumb to go by when purchasing new power supplies is to go by it's weight.

For example, if you buy a 500 watt power supply that weighs 1/2 a pound and a 500 watt power
supply that weighs 3 pounds, you can usually be assured the 3 pound power supply will greatly
outlast the 1/2 pound one.

In most cases, the cheapo junk power supplies don't really weigh anything at all and might only last you
a month or so.The Chinese have figured out this fallicy and are loading their cheapos with LEAD to get away with it...