The scan every 3 days ... that would likely be a full scan, which is good. And the normal scanning, that means it's an active scan, which is also good.
But as I said, no A/V is perfect. And once a virus is in your machine it can easily hide itself from your A/V. MBAM is free (the passive version I mentioned) so it costs you nothing to download & install. Then, as mentioned, it should be run in safe mode (because some viruses don't function well in safe mode). If you wanted to be even safer you could download RKILL (also in the Freeware DB, near the bottom under virus removal).. Then what you would do is install MBAM (RKILL is not installed), reboot into safe mode, run RKILL and then, when that finishes, run a full MBAM scan. Better safe then sorry.
Your problems could also be something as simple as your hard drive dying. Often times hard drives don't just die suddenly, they can just start going bad. What happens is they get bad sectors that no longer properly hold a charge; in which case any data/drivers/programs in that sector could be lost.
You can drop to a command prompt and run SFC /scannow to verify your protected system files are correct.
You can run CHKDSK /r and have it scan the hard drive on next boot to look for hard drive problems.
We're just trying to help you here. We can't see your computer and we simply are trying to eliminate the most likely causes.
