Motherboard wont let me OC all of a sudden?

When i first got my system about 10months ago i had no problem's ocing my e1200 to 2.4ghz at a good temp, volts ect all stable. Recently i found out my cpu went back to its default speed and i cant get it back. My Gigabyte G31M-S2L says its overclocked, but TAT and cpuz both say its still at 1.6ghz. Iv tried updating and resetting bios and trying again, but it still doesnt work. It also sometimes stays on the "windows is shutting down" screen when i try to restart and when i do change bios and hit save-exit it freezes to black screen and i have to reset.

Iv been told it could be my motherboard dying on me, but it still runs and works fine once its on. So i dunno, but im personally all out of ideas. Any thoughts on this?

Full specs:
Intel E1200 1.6ghz
Gigabyte G31M-S2L
Sapphire HD4850 512mb
2gb DDR2 800mhz G.Skill
OCZ Stealthxtreme 500w
WD 500gb Black
Windows XP sp3