PC Peripherals HELP! Change in UPS causes computer to freeze


I recently changed my UPS from APC ES-500 to APC ES-650 and my PSU is Extreme Power Plus 500W (no PFC). After I changed on to this my comp seems to freeze after 5 mins of 4 to 5 mins of activity - nothing works.

After the freeze, I am not able to hard reboot nor am i able to shut it down using the power switch. I have to turn off the PC by turning off the switch in the PSU.

I do not think its anything to do with the CPU/mobo or anything.

Please let me know how to proceed

I'm stumped!


--- Updated Post - Automerged ---

Again, tried connecting without the UPS, I still have the same issue... where should i begin ?? memtest ?