Reinstalling can improve certain things and adding more memory or a bigger hard disk will certainly do you no harm but that may not be necessary.
Try using Windows search/ find files and look for *.CAB and/or setup.exe on your C: drive (assuming your hard disk is assigned to C: on your PC)
If you are using Windows 98, the setup files may be in a folder called win98 (that's the folder name they are in when on the Windows CD) or some people (myself included) often put them in C:\WINDOWS\Options\Cabs.
Before you reinstall you will also need the product code for Windows, so you may need to hunt around in the registry unless you have it written down. If you need help with this post again and one of us will walk you through it.