Half of the time upon power up the program stalls,Other times runs fine. L Flash

I'm noticing in my UNO (Duemilanove)board that as I power on, sometimes times the "L" LED Flashes rapidly then slowly and the program will not run. The other times it runs fine right away. If it gets stuck I can shut down and then power back on and it'll run the program.

What could be happening?

how are you powering it. It could be a power problem. Try to use external power

I have a 5V and 2A supply that I'm using. I also have another Atmel chip in a board (not an Arduino) running another function on the same supply and it never has a hickup.