I'm having a problem with my son's Dell computer. Sporadically nothing happens when the power button is pushed for startup. This first happened after we installed more RAM. Ram chips were matching Dell 524K pair taken from my computer. The unit wouldn't boot up when I pressed the power button. Then suddenly it did boot up and worked fine for a month. Then again nothing. I took it apart and checked out the power switch, got online with Dell tech support. They eventually thought it might be corrosion on a usb port but we were unable to confirm because in the middle of investigating the unit started working. I replaced the USB cable anyway. Now the problem is reoccuring randomly. Any thoughts?

It could be a variety of things:

1. The switch might be going bad.
2. The power supply might be on its way out.
3. For memory, I've always put the largest module in slot 1. For ex., if you have 256MB to start and you add 512MB, put the larger in slot 1 and move the smaller one to slot 2. Also, use the correct memory for that motherboard.
4. Could be a motherboard issue as well.

Make sure the memory is pushed down all the way into the clips.

Try re-seating the memory. May be a PS getting twitchy but I doubt it, they usually just die. One thing to check: Most modern motherboards have a light on them that lights up when the machine is plugged in. This is an indicator that the MoBo is getting power from the PSU.

Thanks for the replies. I had already tried all the suggestions so far. Largest chips in the 1&2 slots reseated everything. Took out the power switch and reinstalled it. Light is on on the motherboard, it goes out when power is disconnected and the switch is held down confirming in my mind that the switch is working. Have been wondering about the power supply and how to check it out and what to do if the motherboard is the problem.

Hmm... best way to see if the problem is the PSU is to connect a known-good PSU to the system and see what happens. Also, try pulling 1 stick of ram, test power, then switch out the other and test power. You will want to test both in the slot facing or nearest to the CPU; this is usually Slot 0. Possibly a bad stick. Can you tell if the fan in the PSU spins when the PSU is plugged in? Have you reseated the power connector(s) between the PSU and MB? P4 MB's have 2 power connectors, 1 20 pin and a 4 or 6 pin for extra 12-volt power.