I had the same thing happen to me a few months ago, I couldn't do anything until I gave my computer a fresh start.
This is how you do that.
Gateway should have given you "recovory disks". One or two based on the amount of pre-installed software. If so there are one of two things you can do.
1. (easiest): If the computer is new enough that it came with recovory disks then start the computer up and put the recovory disk in (disk 1 if there are multiple) and shut the computer down. On some gateways at the start up screen it will tell you to press f2 to boot from floppy/cd and hit "del" to enter cmos (remember cmos for later. It is important if you dont have the recovory disks). Hit f2 or whatever the button is so you can boot from floppy/cd and tell it to boot from cd. A menu should pop up telling you you're about to recover your system and then after answering yes a few times it will restore the computer compleatly to the factory default settings. All software that came with the computer will be installed all drivers will be installed and all your niece will have to do is re-download her internet programs and reinstal games or other programs she may have bought since she got her computer. If you have the disks then you're set if not then read on.
Before you do this check to make sure that you can boot from your cdrom drive by either pressing something at the main gate way screen or by editing the boot sequence in the computers cmos (bios). If not then make a boot floppy on another computer for the operating system you intend to install. DO THIS BEFORE FORMATING!!!!
2. (hard and stupid): First of all, if the computer came with seperate cd's like win 9X and driver disks then gather those up if not then find a full version copy of windows (win98 would do but if you're considering upgrading it might be worth it to buy ME or XP allthough you can only put XP on one computer). Most hardware is Plug and play so if you cant find all the driver disks or dont have any then dont worry just continue on.
Step 1: (format the computer):
*Let dos load and type cd.. till all you see is C:*Type in format c:\ so that it looks like C:\format c:\ and then hit enter.
*it will ask you if you're sure hit y then enter.
Step 2: (booting from the windows cd):
*Now that the HD is clean boot up and enter the cmos like I told you before (hit del or whatever your computer calls for at the very first screen)
*Check and make sure that the boot secuence for the drives are as followed - Cdrom drive (the drive letter), Floppy drive (drive letter A), Hard drive (drive letter C)
*exit cmos and save changes if you had to make any.
*if your computer doenst have that in cmos then you probably just need to hit f2 at the start up screen just like recovering from the gateway disks like I explained above.
*Put the win 98 (or whatever version) cd in the drive and let the computer boot. It should take you directly into the windows setup and install program.
*let windows install and then let it load to desktop. *there should be all kinds of things popping up telling you devices were found, if you can let windows find the drivers on the windows cd and install the drivers.
*depending on if all the drivers were found or not you are either done and just need to reinstall stuff like word or you need to go online for the drivers that were not on the windows cd.
*Drivers can be found
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I had the same proba few months ago, hope this helps
MercuriusX