System requirements:
http://windows.microsoft.com/is-IS/windows7/products/system-requirements
f you want to run Windows 7 on your PC, here's what it takes:
•1 gigahertz (GHz) or faster 32-bit (x86) or 64-bit (x64) processor
•1 gigabyte (GB) RAM (32-bit) or 2 GB RAM (64-bit)
•16 GB available hard disk space (32-bit) or 20 GB (64-bit)
•DirectX 9 graphics device with WDDM 1.0 or higher driver
.... Looks Like you meet Min requirements.
Just a comment/Question. How is your Ram configured? Is it runing Single or Daul Channel? Daul channel is prefered, Reqires Ram installed in pairs and Pair is made up of equal sized ram.
ADDED
If you still have an operating system on computer you can download the advisor (link Below) and it may identify what your problem is.
http://windows.microsoft.com/en-US/windows/downloads/upgrade-advisor