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)

This happened when one of my RAM slots died. There was nothing I could do but use the other one. Note: if your RAM limit is 2GB, you can put a 2GB stick in one. The total system memory, however, cannot exceed that.