So you'll need to check the hardware things like the RAM, HDD and CPU and the easiest way for you to do this is get yourself a copy of the Ultimate Boot CD available free here
http://sourceforge.net/projects/ubcd/
The most obvious thing is test the RAM as you may have some mismatched RAM though generally speaking if that was the case you would get issues as you attempted to load XP not after it's loaded and starting for the first time. Also as this is a E Machine it may be advisable to test the Power Supply as they had a reputation for having weak Power Supplies which could be causing this problem as well.
Col
If you're editing config.sys, that means you have XP installed and it won't start, correct?
Stack overflow is more common when the registry is hosed. Overall my first thought would be if the hard drive, memory, and other hardware is any good or not.
Trying to reinstall XP system but error