I booted the UBCD 511, went to HDD, Boot Management and used PLoP program and booted fine. Rebooted and would not boot. I have no idea what to do from here.
I think that you might have a problem related to the Windows boot files and the MBR / PBR. Using Plop, you have effectively skipped part of the "normal" booting procedures.
Some of the Boot Management tools in UBCD might help you. For example, you have tools to edit boot.ini, or to edit the registry.
Rebuilding the normal Windows MBR and PBR might help you. Only in the case that the problem is not in the Windows booting files, but in the MBR /PBR parts of the booting process, then editing / fixing the MBR / PBR sectors might help.
If you are able to reproduce the successful boot into Windows using Plop again, then this is a strong sign that the problem is located on the parts of the booting process that Plop "replaces".
If your Windows XP CD doesn't recognize your hard drives, then you need some (currently missing) drivers to be included in that CD (or using F6 method) so the HDD (and, then the MBR, PBR and boot files) could be identified and eventually could be repaired.