Try getting into Windows Advanced Options Menu which has other ways of running Windows when it won't start up normally. To get the menu, you need to power off your computer and restart it. Immediately start tapping the f8 key until the Advanced Options Menu comes up. You may find it takes several restarts to get this menu to come up.
your best option if that doesnt work is to just to do a system repair if you have your system disc.
Or you could try and use System Restore Facility through in safe mode if you can access it:
(1) Log on to Windows as Administrator (or as any other administrator-level user).
(2) Click [Start] then [Help and Support] then [Performance and Maintenance] then [Using System Restore to undo changes] then [Run the System Restore Wizard].
(3) On the Welcome to System Restore screen, select Restore my computer to an earlier time (if it is not already selected), and then click Next.
(4) On the [Select a Restore Point] screen, click the most recent system checkpoint in the On this list, click a restore point list, and then click Next.
(5) A System Restore message may appear that lists the configuration changes that System Restore will make. Click OK.
(6) On the Confirm Restore Point Selection screen, click Next. System Restore restores the previous Windows XP configuration, and then restarts the computer.
(7) Log on to the computer as Administrator or other administrator-level user. The System Restore Restoration Complete screen appears.
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Click OK.
there is another way but i cant think how you do it
i had the same problem several months ago, good luck