Remove the disc from the disc drive and clean it with a soft cloth and water. Try the installation again.
Microsoft Windows 7 is installed to a computer's hard drive through different stages, one of which is the expanding stage where the Windows system data files are transferred from the installation device to the computer's internal hard drive. This stage of installation may not complete and remain stuck if certain things within the computer system go wrong. For example, if the computer is experiencing a hardware malfunction, it may cause Windows 7 to remain in the "expanding" stage and not complete.
Verify the computer's RAM is not corrupt. Boot from the Windows 7 installation disc, then click "Next" at the first prompt. Click "Repair," then click "Windows Memory Diagnostic Tool" to check the RAM. If the RAM is found to be corrupt, replace the stick or sticks of memory that are bad.
Listen to the hard drive when the installation progress stops at "Expanding." If the hard drive is making a repetitive clicking sound, it has gone bad and must be replaced.
Replace the Windows installation disc with another copy if none of the previous steps remedy the situation.