Well 13% could be anything. 13% of what?
And to get it back to 100%, to get what at 100%?
I dont think anyone can suggest anything till we know where he got these figures from and what they mean.
Some information on the type of computer (laptop or PC), spec of the computer (cpu etc), operating system (version of windows) and so on.
Also how long he has had it, what he does with it, and what has actually gone wrong.
"cant access certain programs and such" is just too vague.
Does it run slower than usual?, does it crash?, has he changed anything recently (added new hardware or installed a new program).
To give some advice we have to know what is wrong.
Without that I doubt anyone will be able to help.