You have two things you can do,
1: The computer with the problem, you must know what OS version it's running, (eg. 64bit or 32bit of Windows 7)
2: Then go to any other computer that has windows 7 **bit (** stands for the number of your previous not working computer's bit. eg. 32bit)
3: Insert a blank CD/DVD in your computer (minimum 500 mb)
4: Go to start in the other computer, and type in "create a system repair disc" and press Enter
5: Then Select your CD/DVD drive in the select option and click Create disc
6: Restart your computer
7: Boot from your CD/DVD by press F12 in your keyboard while booting up. (Might be different key for other computer. If it's different for you, go into your bios and enable your CD/DVD to boot first)
8: It should say "Windows is loading files" like how you first were to install Windows 7
9: Then you should know what to do. If not, tell me and I will tell you next steps.
1. Get your Microsoft Windows 7 installation disk ready.
2. Boot from it. Then follow step 7 in method 1.
Let me know if it helps you. If you succeed in these steps, then click on "Startup Repair" in the option when the disk loads up. It should fix the problems and ask you to restart the computer.