I've had my arduino uno for a couple of months but then just today it quit allowing me to download any new programs on it. In the bottom right it says ardunio on com 3, but under tools/serial port is completely grayed out. I know that i did not blow anything as the last program on it still works. I checked the drivers, and they are up to date. I am stuck at this point trying to figure out what to do next.
Damaged components don't always fail immediately. It's possible you damaged the USB to serial chip in the past.
Have you tried the loop back test.