little sparks when plugging in usb

hi,
recently i was plugging a usb receiver for a wireless desktop into the back of my pc and i thought i saw i tiny spark just as i put it in, but i wasn't reeaally sure and ignored it.

then today, i plugged in the cord for a usb hub to an adjacent usb slot (i didn't notice any spark but i wasn't really paying attention).

the usb hub (belkin 7 port hub) worked for a few minutes then nothing. no little led lights or anything. i disconnected it and just tried plugging it into the mains without any connection to pc and still no power at all.

so, should it be possible for sparks between back of pc and usb plugs?

do i have a power problem?

thanks
trent lane.