Fist thing to check is whether the Drive is detected in BIOS.
Change your Boot order in the BIOS to CD/DVD Floppy HDD save the settings and exit the PC will restart.
Put the Drive back in the PC that you used to install XP. Insert your XP CD and when you see ?Press any key to boot from CD? press a key. Click Install Windows XP. In the Windows Setup window, click Upgrade (Recommended) in the Installation Type list, and then click Next.
Follow the instructions on the screen until the computer begins to restart. Just as the computer begins to restart, turn off the computer. Remove the Drive and put it back in your PC. If all goes well setup installs the HAL, the IDE controller drivers, and any other drivers that the new motherboard must have.
After the upgrade is completed, reinstall any service packs or hotfixes that you had previously installed. Install the Motherboard Drivers for your PC.
If it is still not Booting try this.
Insert your XP CD and when you see ?Press any key to boot from CD? press a key. Now wait for the XP installer to finish loading up and you will be presented with the option to press R to Repair.
Press R.
The next screen will ask you which Windows? installation you would like to log on to. Normally the following will be listed:
1: C:\WINDOWS
Press 1, then Enter to continue.
You may now be asked for the Administrator password. If you know this type it and press Enter. If you don't know the Administrators password it may be blank. Just press Enter or type your username and password.
At the command prompt type:
fixmbr and press Enter
fixboot and press Enter
Wait until you are returned to the Recovery Console.
Type bootcfg /rebuild
Once you are back to the Recovery Console remove the XP CD and restart your PC.
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