PIC16F877 not executing?

[Ian Curtis]

I realize this is kind of a long shot, but I've got the PIC in a breadboard that worked perfectly fine yesterday, using the same code that worked yesterday. I pulled out a soldered contact carrying the power supply, and didn't bother to fix it until today. But after fixing it, I don't think the code is executing. For some unknown reason, the debugger is giving me an MCLR error which I can't seem to solve, but the ICD works. It downloads the code without a problem, but when I try and run it, nothing happens. When my original code (which is supposed to control the robot based on an ultrasonic sensor) did nothing, I figured perhaps I made a mistake, so I wrote something to make an LED blink, which didn't do anything either. I checked the pins with a voltmeter, just to make sure, and didn't see any change. Also, I checked the power rails, and those are fine (+5 volts). Just for kicks, I plugged the motor controller into +5 volts, and it worked fine. I checked multiple times for loose wires, and found none.

If I fried the PIC, the code wouldn't download would it?

Is this a symptom of some other error?

I thought the most likely thing would be that I just wasn't plugging things in the right places, on the breadboard, but I've checked that more times than I can count, and tried placing them in other slots just to make sure, and there was no change.