We tried to upgrade the computer to run Flight Simulator FSX faster and it didn't seem to work. Current Processor runs at 2.67Ghz so that might be part of the problem. Put 8 Gig of ram at 1333MHz (may be too slow too) a new graphics board: Radeon R7770 and new power supply. Going back to Best Buy to return upgrades and buy a new computer if the processing speed is the issue. Programs take forever to load and hang up at times.
Is there a question in here? From the sound of things, you just need to re-install Windows since you have stability issues, not speed issues. Anything that is running slow is due to bad configurations or too many programs running or a virus (or 5).
Flight Simulator X came out a while ago, just about any system made in the last 4 years will be able to run it if it has even a low end gaming card.
You did not list a lot of info as to exactly what CPU you have now, what XPS model is this? You seem to be spending a lot of time on trying to fix the wrong thing from how you explained things.