I just recently built a computer for somebody and am having a problem with it not wanting to power up correctly. When I press the power button, the computer comes on, but doesn't POST. The HDD, CD-RW, fans, etc come on, but the monitor remains off, and the computer goes no farther. When it does this, if I press the reset button, most of the time it will start up correctly... POST and boot up to Windows. The CPU is fine because I can boot up and run Windows with no problems if I get past POST. The video card is fine as well because I took it from my own machine. The monitor works because I've tested it on another machine and it works on this new machine if it POSTs. I've tried clearing the BIOS, and that doesn't fix the problem. The only other things I can think of that could possibly be wrong is the power supply or the mobo. Anybody have any suggestions as to what's causing this problem?

Sounds like the power supply's a bit too weak for the PC components. What wattage is it?

Power supply is 300 watts. The computer doesn't have very many components in it. It's very similar to my own machine, except it's got a 1.7 Celeron processor and mine has an Athlon XP 1900. Does a Celeron 1.7 system need a higher wattage power supply than a 300? Should I try a 400 watt?

Depends really on whether the 300W PSU is of good quality or one that came with a cheap case. Before looking into a new PSU take a look in the BIOS, in the hardware monitoring section, if your board has this, and see what levels the following voltages are at. +3.3V +5V +12V If either of those rails is 5% over or below it's rated amperage then the system may have stability problems or booting problems, although the problem with yours is that the PSU could be slightly weak on one or more rails. When the system is powered on from cold this is when the PSU has to be at it's best as this is the time the components, especially the harddisk need the most power to spin up properly.

Yes, the PSU is one that came with a cheap case. I just checked the voltages in the BIOS, and it looks like you're suspicions are correct. The +3.3 and +5 are ok, but the +12v kept wanting to go all the way down to 11.37. This appears to be what's causing the problem, a weak PSU. Looks like I'll be replacing this cheapie with a better PSU. Thanks for your help Ben!