I have been using an Arduino Uno R3 to operate a small sevo off the arduino 5v and it worked well for awhile but now it doesn't move even with the same code Later I noticed an article that said that the servo must be powered with an external power supply or battery because the PC USB port can't supply enough current to drive the servo, but it was working just fine for a month or so. witjhout those. Is it possible that I messed up my arduino? Any ideas?
Anything is possible. Troubleshoot the problem one item at a time, each by itself.
Do you have a multimeter to test the Arduino 5V regulator pin?
Do other devices work plugged into the same USB port?
Do you have any other way of testing the servo such a hobby grade RC car?
Debugging steps.
You say it's not working. Try downloading the basic blink.ino (included with the IDE install). If that works, then your next step is to verify your servo output works - maybe wire an LED with series resistor to it, and modify blink.ino to toggle that pin.
IF those two tests work, then your servo may have quit.
Good luck.
Some of those small servos do not like to be stalled. If held against yheir stops for too long they will burn out. Do not run them stop to stop (0-180). I experimentally measure each one's travel and mark it on the servo.