Why is my MacBook Pro quitting and/or failing to start up?
The blinking is a for of POST (Power On Self Test) and can certainly help diagnose the issue.

As most people are saying it is most likely a RAM issue.

The following documents can help diagnose POST messages and various issues related to your laptop during the boot process:


Intel-based Mac: Startup sequence and error codes, symbols
Intel-based Mac Power On Self Test RAM error codes
Your Mac won't start up in Mac OS X (Mac OS X 10.3.9 or earlier)