Dell Dimension 8400 resotre or reset?

I have a Dell Dimension 8400 desktop computer and have been having some issues with it lately. It runs very slow and takes a long time to startup as well as open new programs, and even on the internet it is slow. Also there are frequent error messages about debugging issues and other things that seem to hurt the smooth running of the system. Even some of the programs are beginning not to work. I defrag frequently, but can't seem to solve the problem. I was wondering if there was some sort of restore or reset method of the ram or something to fix the problem, or if it is another problem all together how to go about fixing it.

I know what you mean about slowing down! Mine does the same. All I do is go to Microsoft Cleanup Center to clean the registry and that seems to make the biggest difference. You also may need to clean off a lot of spyware. I find the AVG free version works very well. Another possibility is to try to limit the number of programs that start on start up. Good luck. I hope this helps, let me know.