Why will my desktop not detect any cameras?

This morning I tried to copy some photos from my Nikon Coolpix onto my computer but the camera was not detected. I have also tried to connect 2 other cameras which are not recognised either. If, however, I plug them into my brother’s laptop then they work fine.
Also, if I plug any other USB device into my computer they work as normal – it just appears to be my cameras that are not working.
I have never faced this problem before and have tried different cables and different ports but still no cameras. I have also tried to connect them on both Ubuntu and XP but both systems are ignoring them. The problem is obviously not with them as they still work on the laptop.
Any suggestions?