When I inserted a 4GB Mikomi USB memory stick into my computer's usb port, my desktop switched off instantly. The system will now not power up. Not even the fans spin. I have unplugged all my other USB peripherals but the problem remains.
Do you think it is more likely that the memory stick has killed the PSU or the motherboard, or might the power problem be something else?
It was a brand new memory stick and the problem happened on the very first installation attempt. The motherboard was about 4 years old (L7VMM3 from Elitegroup) and one of the USB ports was already damaged, although I did use a working port with the stick. The PSU was about 2 years old and unbranded.
It is possible that static electricity could have made your computer switch off.
It is also possible that 4GB presents a larger load than a 128 MB thumbdrive would present based on my theory that there is more chip size. I have an old 128 MB thumb drive and for some reason it gets warmer in newer computers and that may be due to the internal temperature of the newer computes but we're trying to get electricity to go through more silicon and newer computers seem to have beefier power supplies for the new power demands. To get all of the power down to the small requirements that a thumb drive requires seems to tell me that if the electricity isn't regulated perfectly, it is always possible to have a problem.
My 2c worth, since you get no fans spinning or anything when you try to start up you've fried either the PSU, Mobo or both. The power drain off the PSU with another USB device may just have been the straw that broke the camels back. Then again you did mention that you had other bad USB ports on the Mobo, that may have been a sign that you're Mobo was on its way to the big silicone factory in the sky.