The reasons are tabulated below.
1. HDD or SSTD has run out of space.
2. Hardisk Drive is corrupted.
3. Insert other Windows disk.
Format the harddiskdrive partition and insert the installation disk to continue and when prompted, make three to four equal partition or as per your requirement and space preferences.
Delete the BIOS password. Boot the computer with installation disk, press the Esc key repeatedly while booting to enter setup. Chosse the boot with Hard disk name, press down to administrator password with the navigation key ane enter to remove password.
If nothing of the above steps work, visit deohut dot wordpress dot com, navigate to OS tutorial and read the artilce on how to make a bootable pen drive to install Windows along with other PC's related issues.
Be the Hero of the zero hour!