Motherboard or CPU Problem in Overclocking

Yeah, so i have an asus M2N-SLI Deluxe Motherboard Latest BIOS (which is something like 0903)

And my CPU is AMD Athlon 64 X2 4600+ (not the low Wattage version)

And my PC has been working great!, no problems, everything is smooth, but i decided to Overclock and I can't! i go to AWARD Pheonix BIOS and Jumperfree set to Manual, Multiplier to 10, 11, or 12 and frequency to 235,240, etc.. and when i save and quit, my screen goes blank.... i restart and i have 1 long beep and two short?! ,(Due to a video card problem im using a PCI video card (soon to get 8800GTS).)

I dont know whats wrong why does it not work, someone mentioned that a PCI video card can cause overclock problems to CPU but i dont know.

Is it still possible for me to overclock?

just try the frequency first, dont worry about multiplier,

And turn on "AGP lock" or "pci lock" if your bios has it, if not try and find a newer version that has it,