OK here is my suggestion:
Take your motherboards manual and look for the motherboard blueprint, on it look for a jumper called JMOS or CMOS or CCMOS, something with that combination of words [if you find the JMOS, then right next to it should be the CMOS]
Look for instructions how to set up the jumper on the motherboard so it will short the cmos and restart it [It will wipe all the current configurations and restart everything back to defaults on the BIOS], once you put the jumper on clearing the cmos configuration, power up you're computer for 10-15 seconds and then shut it down by pressing the power on/off button for 10 seconds, then replace the CMOS jumper on its default settings and viola.
Why do I suggest this? Because this sounds like your bios is stuck on the bad OC settings, although you lowerd the FSB on the BIOS it sounds like it didnt really update or theres some left overs of the OC that caused the problems, this should fix it completly.
Heres another method if you do not know what is jumper or where the cmos jumper is, or what to do with it once you find it:
There is a Lithium Battery on you're motherboard, like big clocks battery, what you do is remove it [carefuly, dont break its socket] and disconnect youre computer from any external power source [AC cable that connects into your PSU>>Disconnect it]
This will ALSO wipe clean you're bios/cmos BUT IS LESS RECOMMENDED! [Not that its so bad, but its like restarting your computer from the Reset button, doesn't harm all that much but is not recommended to do]
Please report to me of how well did this work for you,
Good luck,
-Jo.