Do you have the latest P8Z68-V PRO
BIOS 0706 update flashed?0706
makes the following changes/fixes:
1. Fix FW54P PCI card compatibility issue
2. Fix the bug that the OEM activation version OS of window7 will hang at the "blue screen" if some graphics cards be installed in system.
3. Fix USB Keyboard 3R-FKB3010UBK can't work issue
4. Fix Microsoft V1 receiver can't work issue5. Fix S3 can't resume if CPU PLL over voltage is enabled. <--- This one most likely applies to your problem.
6. Fix the CPU and Chassis Fan speed will over the duty cycle setting range.
7. Fix CPU ratio always keep at lowest after S4 resume and AC power lost.
8. Improve DRAM compatibility.
9. Support new CPUs. Please refer to our website at: http://support.asus.com/cpusupport/cpusupport.aspx?SLanguage=en-us