Arduino IDE Glitch/Extreme Annoyance

Sometimes, when trying to upload some code, the IDE would randomly state that my serial port (COM3) wasn't found. No programs other than windoze junk and a Bukkit Minecraft server we're running. I know my drivers work, unplugging/replugging the arduino doesn't help either. No Device Insertion sound is played, and the Loop back test failed. The only way to get it working again is to reboot my computer, which takes too long. Any help here? it's a real pain...
Windoze 7
Arduino UNO R2
IDE 1.0.5

Note: It doesn't show up in driver manager/devices and printers either. :frowning:

Edit: The Pin 13 LED isn locked on too...hmm! It also seems that the Ethernet shield resets the arduino when something is received, or maybe that's just my software.