I have used MyDefrag following recommendations at http://www.techsupportalert.com/best-free-disk-de-fragmenter.htm
I did run it on Win 7 64-bit in my main HDD and used the monthly system disk defrag option on the system disk with a Win XP 32-bit system on it that I had mounted in an ultrabay slot. Afterwards, I tried that disk in my main HDD slot and it did not boot. However, it worked still fine as an external/ultrabay HDD until this morning. When I booted my Win 7 system, it detected data corruption on the Win XP 32-bit partition and ran a fix. After this fix, I cannot access that anymore.
Please help me troubleshooting this.