Sounds like your boot.ini file is pointing to the wrong partition. with os hdd only, start up and go to notepad and go to file, open, boot ini. it should look like this:
[boot loader]
timeout=0
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect
if not, rename your boot.ini and save it and try editing with these values. Make a
ASR (automated system recovery) disk set first to avoid any problems.