Although the reason caused this problem is still unkown...I should be aware of that in case it might happen again.
- Put the Windows installation CD into DVDRom then restart.
- Let it scan the PC, then choose R to recover.
- Choose to identify the existing Windows system.
- Or type in:
C:\BOOTCFG \LIST to list all booting system
C:\BOOTCFG \ADD to add one booting system or
C:\BOOTCFG \REBUILD to rebuild the booting .ini file.
- Note that the BOOTCFG "Identifier" is the identifier like "Windows XP Professional".
Now restart and enjoy.