To get better help/suggestions, include some information about the PC that you are having problems with.
Some info needed:
The computer make/model, any upgrades, or other changes from factory spec
or if the PC is custom built

The Motherboard make/model boar revision number and the bios version.

The brand/amount of ram installed
The brand and model of CPU
The brand/model optical drive "cd/dvd"
The brand/model videocard
The brand/model and wattage rating for the power supply.

In the mean time, check that there are no scratches or dirt/finger prints on the installation disc. If the disc is dirty, it can be cleaned with warm water and liquid dish soap, then dabbed dry with a clean towel, then dusted..
If the disc is scratched on the bottom/read face, it can be buffed, if it is scracted on the label side and you can see light through the scratch from the bottom, the disc is no good. If the disc is clean and not scratched, ensure that the hardware is clean; check the components for dust buildup, if dust is found on the cooling heatsinks, and or system board/components, clean it off.

Ensure that the computer is not overclocked while installing windows.

Also, try reseating the ram by unclip the side tabs, then pressing the memory back in till the side tabs click back into place..