Your computer needs rebooting after a couple of approaches and landings using Microsoft Flight Simulator ninety eight, or a few hands of solitaire, etc. in usually about twenty minutes. It just gets slower and eventually freezes. Your computer is running Windows XP operating system.
You contributed to its demise by fiddling with a couple of data codes in DOS. Then you compounded errors by uninstalling Norton Anti Virus and installing Avast. Then it began to grind to a stunning halt every few minutes.
You can only receive a few e-mails and respond to some before it gives up. Looking at cars for sale on AutoTrader.com is a nightmare. You look at a car's enlarged specifications with several photographs and all you get is about four cars and your computer freezes and you have to reboot.
There are a few things you can try. I suggest running a chkdsk scan, running a Malwarebytes scan, and cleaning your personal computer and registry with Ccleaner. Boot your computer into safe mode with networking by hitting your F8 key after the BIOS screen flashes and before Microsoft Windows tries to boot and then selecting “Safe mode with Networking”.
Once in safe mode please download and install MalwareBytes to get rid of malware. Please update, then run a scan for viruses, malware, and adware with that program. Another program I recommend is to download and install CCleaner.
Use Ccleaner for cleaning your personal computer and registry cleaning. Finally, go to "Start" then select "Run" and type in cmd into a run box. In a black command prompt window type in: chkdsk c: /f /r.
A chkdsk scan might take awhile. Type Y at prompt to schedule a chkdsk at next reboot. Reboot your computer and chkdsk should start it's scan. Another scan you run is a system file check scan.
Type sfc /scannow in a command prompt window. You may become prompted for your Windows installation media.