dendol, hi, the problem you pose may not be cut and dry. The problem could have a lot of causes. But before you replace the motherboard, I suggest the following:
Purchase a multimeter at RadioShack or the like for about $20.00 to test the power supply. You can find a lot of info about it at
http://www.doctronics.co.uk/meter.htm &
http://mechatronics.mech.nwu.edu/mec...ultimeter.html.
But have you gotten a new round-shaped Lithium battery yet? Most of the time, it should say "2032" on it. But whatever the number type of battery it is, it costs about 2 or 3 bucks at your local CAMERA LAB store. I'm presuming, of course, you have the modern or ATX motherboard right? If you have an old, I mean really old computer like on some x86s , the cylinder or the DALLAS-brand type of battery is soldered in, in which case, it is next to impossible to replace it.
Next, if the new battery does not work, just leave your computer alone for up to 10 days or so, with no battery in the battery compartment, so that the circuits are completely discharged. What happens is you may have accidentally bump into some circuits while re-setting the CMOS jumper, for example. After the 10 wait-out days, your computer (power supply) may miraculously come back alive. There were times when I waited 30 days or so just so the motherboard is completely discharged!
Then next, check and re-check your motherboard jumpers with the manual. But then again, if your power supply worked, say, yesterday, and not now, then you may have accidentally zapped your motherboard with static electricity, especially if you are working on a carpet with no anti-staic wrist wrap or FARADAY ANTI-STATIC MAT.
Next, try removing some power cables from devices you may not need yet, such as from the other 2 or 3 fans you may have or, even the extended Y-SPITTER cable.
Next, check to make sure all your computer parts are firmly seated in the slots, connectors, etc. or firmly snapped in, especially your DIMM, DDR or whatever type of memory card your motherboard have. Memory cards that are NOT firmly seated onto its DIMM or other type of slots can cause all sort of nightmarish problems. This is especially true if the memory card (s) have different memory bus speeds or is not recommended for your particular motherboard. :) ::)