|My first thought (from experience working with these Dell Models,) is that the MOBO is going bad. The 270s and 280s are notorious for that...|
A new board would cost a few hundred dollars.
The other cause could be that these models are not supported in Windows 7, so you probably don't have all the correct drivers.
You could try reverting to Windows XP and see if performance is any better. You may just be better off just getting a new computer, especially since this one is several years old.
Also, It's not a good idea to include your email address in plain text, and since this is a public forum we respond here; personal replies via email are not really the norm here.