Ahhh - computer hangs

[fatt_fill]

Firstly I'd like to appologise if anyone feels that I'm posting in the wrong forum. This problem could be software, or hardware, but the OS is XP, hence why I posted here :-)

Ok - heres what happening. A friend asked me to look at their PC because it hangs frequently. If they unplug the modem (external USB NTL Broadband modem), then all is fine and it never crashes. Suspecting that something was wrong with the drivers, internet services etc etc.... I formatted the C:/ Drive and reinstalled windows (XP Pro). But the problem still occurs :-@

After a bit of fiddling here's what I have discovered.
The problem just started occuring a month or so ago, and to my knowledge did not correspond to any new drivers or windows updates that were applied.
If you unplug the USB scanner, you can use the USB modem with no crashes - so it seems to be when you plug in lots of USB devices it crashes.
The PC is pretty mad though - it has four USB devices, one SCSI, and a card in each of it's 6 PCI slots.

My theories are as follows:
Resource conflict (IRQ??) - maybe as their is so much kit plugged into the PC it can't handle it all at once.
Power demand - I believe the PC has a 300W PSU which at the time was pretty meaty. Now I'm wondering whether this is enough.

Any comments would be greatly appreciated.

Thanks in advance,
Phil

[reboot]

You could be on the right track.
First, I would check IRQ assignments. Although XP handles things better than other Windows OS's, it could be a problem.
I would bet it's a power problem. Even a 300w may handle the drain, but not if it's a cheap supply, or cannot sustain the minimum wattage/amperage while all devices are running.

[KHT]

USB is *supposed* to run all devices from a single IRQ. Are you using an external USB hub? If so is it powered? The external hub, if installed, could be the problem. I ran into a similar problem with a USB mouse and had fits until I discovered the external USB hub was the problem.

[fatt_fill]

Originally all the devcies were plugged into the USB sockets on the MOBO, or on the USB bracket off the extra USB header on the MOBO. I tried removing the bracket, and putting in a 4port USB card that I had to see if it "shared the load" better, but it still crashes. I suppose I could try the latest 4 in 1 drivers, but then I don't see why when I used the PCI USB card it still would have crashed.

My plan of action is to try my 550W Q-TEC PSU in the PC, and if that fails, advise that they buy a router - having to have to "main pc" on so that the other computers in the house can share the internet connection was always a hassle anyway, and by taking this responsibility away from the machine in question it will stop it from crashing. It just doesn't really solve the problem - just avoids making it happen......if that makes sense.

Thanks to all for your help.
I shall have a fiddle next time I see the PC in a few weeks and report back if I have any luck.

Cheers
Phil