Raspberry Pi Won't Boot, Red Power Light Only (update)

Yesterday one of my Pi worked perfectly, but today just the red power light turns on. There is nothing through either HDMI or Composite outputs and the OK light bearly turns on.

Yesterday it worked with a 32GB SD card, Logitech wireless USB keyboard, , Amazon 5V 1.8A charger for a Kindle.

I tried re-flashing the SD card and tried a Lexar 4GB SDHC Class 2 card and neither worked. Unplugging everything but the power and SD card didn't work either.

Reading about this problem on various forums it seems to be quite common so I will need to play about with the raspberry Pi and try and find out what if if I'm able to bring it back to life.

(Update)

After much playing about and messing around plus reading the many Raspberry Pi related forums (raspberrypi.org is the best). I discovered that there were infect 2 faults with the raspberry Pi in question!!!

1) A broken SD card socket. Currently using a match stick to hold the SD card in its socket

2) The SD card that wasn't compatible but it didn't initially say on the list, the list has been updated since I initially looked.