What windows are we talking about?
Are there ANY messages?

In case of XP:

Boot from XP installation CD (please post if you need detailed instructions)
When prompted, select -r for repair mode
You will be prompted for Admin. password.
type "CHKDSK" and hit enter. This will fix the errors on your HD that occured when the power outage happened, hopefully fixing the problems with windows.
When finished type "exit" (maybe it is "quit", cann't remeber) and it will restart your PC.

There is allways a choice of disableing the automatic system restart (f8 menu) that may start the windows with some problems left, which you can access via device manager (right-clck on my comp., select properties, click on hardware tab, click on device manager button and post any device with exclamation mark on it)

If you still cann't boot the system, only choice left is to reinstall the windows (sorry).

In case of Win95/98 do the following:

Hold f8 when booting, and select command prompt.
Type "SCANDISK" to fix any error that occured with this power outage.
when finished reboot the system.

If that don't do the trick, try (repeat the above step)
Type "CD WINDOWS" (giving that "WINDOWS" is your windows directory)
Type the following:
attrib -h -s -r system.d*
attrib -h -s -r user.d*
ren system.dat system.bad
ren system.da0 system.dat
ren user.dat user.bad
ren user.da0 user.dat
Now reboot the system. (ctrl-alt-del, not the button)

I would be happy to try this, but I don't have the installation cd for windows. A friend built this computer for me (we now live in different states) and he didn't give me the disk he used to install windows xp.