What you have done is corrupted the master boot record of the drive.
Windows needs this in order to load.
It contains data as to where to find and load files in order to run the installed os on the drive.
When it becomes corrupt, no bot-table os will be found on the drive.
To fix it, you can use a windows install disk, and use the repair tools option.
If you have a windows xp disk you can use that.
You need to run a command prompt.
And type: Fixboot.
Then type Fixmbr.