2 problems, Hard drive space and blue screen

First off, thanks for taking the time to read and hopefully provide a solution!

Background: 2.5 year old acer 4937g laptop.

Problem 1: Acer laptop C drive experiencing flucuating free space between ~5gb to ~800mb.(but mostly between the lower end of 3gb to 1gb free space left.)
Has max capacity of 60.1 gb. Total used space is 51.3 gb. So where did all those missing space go?

Solution tried: Disk cleanup & defrag, Check disk, removing system restore points. None worked.

second problem: On the same laptop.
Experiencing increasing amount of blue screen errors. I think my computer has at least blue screened 20(?) times during the last 5 months.
Prior to this sudden increase. I've only experienced it twice over 2.5 years.
I've tried virus scans, but half way through it blue screens, so im looking for any sort of help available.
Once again thanks for taking your time to read!