What is the make and model of your graphics card? The Intel 845 chipset is, I think, a Pentium 4? I'm not really sure if your computer can meet the minimum system requirements to run Windows 7 (I could be wrong though).
Windows 7 Minimum System Requirements:
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
Go to intel support and run the driver update tool. Anything that needs updating (and available) will be listed for you with a convenient link to install immediately. Since the 845 is older there may be a compatibility issue though.