Don't leave a usb key plugged in when booting!

Had a bit of a scare tonight when booting up the xp machine tonight - it got as far as the boot screen and then froze - no countdown of the 5 seconds before an os option was chosen. Took me a while checking the fact that the disk was still intact, the keyboard/mouse was working until I spotted my pendrive in the usb port. Removed it and up the machine came - phew! I was REALLY hoping that it had nothing to do with the new psu I had installed on Friday night, hoping it hadn't blown the motherboard or something vicious.