Flashing L LED When powered, Sketch doesn't load

So one of my arduino's has started acting funny, and I'm not sure what to do since the troubleshooting page doesn't seem to mention it.

When I first plug it in, via 9v or USB, the sketch won't load and the L LED flashes three times rapidly. When I upload the sketch to it again it seems to work fine, until power is removed. Plugging it back in, and I'm back to square one. I'm still very new to this, so any help would be greatly appreciated.

There were some bootloader issues with the new Uno board - what serial number is your board (I presume it is an Uno)

Is it an Arduino Uno SMD? Where'd you buy the board from?

As mowcius says, the bootloader on the ATmega328 on the board probably has a bug that causes it to go into an infinite loop when you unplug and replug it, meaning your sketch never starts. We've since fixed this bug, but a few of the boards were sold with this problem. You should be able to get a replacement from the distributor you bought it from? Or, if you have an AVR in-system programmer, you could flash the new bootloader yourself.

Yes, it is an SMD edition UNO. I don't have an AVR programmer, would I be able to burn it using my other Arduino?

AcidFire:
Yes, it is an SMD edition UNO. I don’t have an AVR programmer, would I be able to burn it using my other Arduino?

Pretty sure you could program it using the arduino ISP sketch