[Belial]

Two questions for you.

What RAM does it have?
and
What kind of hard drive does it have?

Sometimes, just buying a better RAM can fix the issue of lag and freezing. The ones I had to purchase for my older computer was $50 but the newer ones are more like $20. I saw this on a Tech website I frequent, regarding a model just like yours.

RANDOM FREEZES FIX:
My computer used to freeze randomly until I fixed the memory timings. I suspected bad memory early on and tested it with MEMTEST, but it passed with flying colors. I even tried swaping memory out, trying to eliminate bad memory and/or slots. It turned out that it was a memory frequency/timings/voltage issue. No more freezes! If you have a similar setup, this will most likely fix it. If not, then check your memory and/or power supply.

And if the hard drive is only like 350gb, that isn't very much at all. If you suspect a virus though, you can try AGV or Malwarebytes. Both are free and I have heard nothing but good things from other people. I use it myself, haven't had any issues with either.