clone HD with nvidia 680i lt SLI

I have a Systemax Venture N2000 running XP Pro with 4GB of memory.
I back up the entire hard drive by cloning to another drive and have had no trouble until recently.
Last couple of times I hooked both (identical WD 80GB) drives and boot up I either get a blue screen of death or get a boot into the desktop but the system is very slow(cpu usage 80-90) and will run for a few minutes before I get the BSOD with a "bad pool header" error.
I have the latest BIOS and have reset it to defaults and have not added any components since I was able to clone sucessfuly.
Virus scans are clean and the computer runs just fine on either drive when only one is connected.
I'm not using raid, only one drive at a time except when trying to clone.
Any ideas?