After reading this thread, I don't know what you really tried and what you just say that you tried, or glossed over. Please do try these, people here in general have given you good advice.
Here are some steps to summarize:
Boot from a cd or USB stick with memtest86+ on it. Run that overnight or at least until it completes three complete sets of test. That should rule out RAM errors and likely motherboard errors for the most part.
If no errors, check the hard drive next. It sounds like you already have checked the SMART tests, you should run a full check disk as well with "check for bad sectors" checked off and have it set to run at next boot, then restart and let that run.
If that finds no major errors, It is time to backup important data, format the boot drive and then reinstall using a fresh copy of Windows or your manufacturer restore disks. Remember to run Microsoft update to patch and update Windows. Next run Prime95 with all four threads in RAM enabled. Let this run for 12 hours and check temperatures. If not over 80 degrees C on the main core, that should be OK.
If you do not happen to find any errors after all of this and your computer still seems borked, its time to hire a professional or buy a new computer. Probably cheaper to buy a new computer.