|A few things affect booting. Bios settings are normally the first place. Use boot order to select hard drive first. Might as well disable lan boot if possible while you are there unless you use PXE.|
Second is the way the hard drive is loaded. A few things there can cause this. There has to be an active parition and the master boot record has to be correct to load the OS.
My guess you need to fix MBR first. Then might have to do "repair" from xp cd.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10