just a tap to the case and system freezes

I sat down to my brothers computer and taped my knee on it and the desktop freezes, and no mouse or keyboard. Also the optical drives restart and the hdd light on just on and no flashing at all.
Opened the comp up and checked the connections to all devices and mobo from the PSU and all is connected well, no probs.
So I'm thinking power supply unit problem. Somethings gotta be very loose inside the PSU.
Just so you know the comp is an Asus p4c800 w/Intel 1.8 and gig of ram. Also a MSI mx4400 128mb, 2 optical drives, 1 hdd powered by a 300 watt max generic PSU.
I can't think of what else the problem could be. If I had an extra PSU I'd try it but I don't.

I'm just looking for some other possibilities to the problem and/or solutions before we buy a new PSU in a few days.

Thanks in advance all
even though I'll prolly have to buy a new PSU

 

Hi,
What happens when you start the computer?
I take it that the screen stays blank, the fans run, some lights flash, but the HDD led stays on solid.

You could check the PSU voltages using a multimeter. The red wire is 5 volts, the yellow wire is 12 volts the black wires are ground.

I would be more inclined to think it was a loose connection. Pull out and reseat the connections. All the connections, optical drives, floppy drive as well as the data cables to those.
You can leave the power and data cables to the HDD disconnected and try starting without it. See if it gets video so you can go to the BIOS settings. Make sure the HDD is not listed in the IDE configuration, save the settings, shutdown and reconnect the HDD. That will ensure that the HDD is reconfigured in the BIOS.

Calculate the power consumption:
http://www.jscustompcs.com/power_supply/

I might be inclined to reseat the graphics card and PCI cards as well (also the RAM stick/s if you are on a roll ).

Matt

 

I have seen ill fitting power cords work loose from the PSU. A little tap is all it takes to cause a poor connection.

 

I would go with something being loose; or something shorting when it moves. Tracking it down is going to be an involved process since it could be a loose motherboard, processor, hard drive, ide cable or any of a number of other parts which just gets loose enough to cause a system problem and reboot.
If XP, have you gone to control panel/ system/ advanced/ startup and recovery / settings / system failure
Uncheck restart on failure.
check create log file
check send admin alert.