You may need to edit your boot.ini file now...
Control panel, System, Advanced, Startup and Recovery Settings, Edit ... the boot.ini file so it looks like...
[boot loader]
timeout=10
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
OR...
[boot loader]
timeout=10
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Home Edition" /fastdetect
IF... you have installed the Recovery Console on your boot drive there will be an additional line...
C:\CMDCONS\BOOTSECT.DAT="Microsoft Windows Recovery Console" /cmdcons