OK, so you have the DVD of Windows 8 to install yes?
Well then, it's not too incredibly difficult. Pop the DVD into the laptop, and then boot from the Windows 8 DVD. Click on the agreements and such, and when you get to the screen that says Install Windows, there is a little link on the bottom left of that window that says Repair your computer. This takes you to a light blue screen. Click on Troubleshoot, then Advanced Options, then try Automatic Repair. If that doesn't work or just seems to take WAY too long that it should, a different method will need to be used.
Next method to use will be System Restore, it's in the same list of options that Automatic Repair is in. If you have a restore point recorded on your PC, try the most recent. If that doesn't work, a different method will need to be used.
The other method is Refresh. After you click on Repair your computer from the install window, hit Troubleshoot, and you want to try Refresh your PC. This one is a little more dramatic as this removes your Desktop programs, defaults any changed Windows settings, but it'll make a folder (once back into Windows 8) called Windows.old where you can find a list of removed Desktop apps. It won't erase your user data and customization settings though. Hit Next, and it'll refresh. This might take a while. I recently did this the other night and it took about half an hour on a system that I just cleanly installed Windows 8 on, but the NVIDIA driver went awry. It'll depend on some things on how long it'll take. Just let it do it's thing, and hopefully you won't need to use this option, but if so, hopefully it works!