Internal drive lying about low memory ?

Okay my computer I have windows vista and I had a virus at one point and I called the Dell ppl to see wat they would say and they said I should reinstall windows well that ended up making a bigger problem for me now >.> since when I did that I magically put the older windows files like program wise which I thought it would delete and just have a clean disk back on my computer and made it as a fake file which I had removed by a friend who works on computers and then that's were my troubles started when it said it had magically no space on my computer after removing a bunch of files ? so now idk really wats happening one day I had half memory and then poof I had none ( after my mom bought two RAM bar thingys ) and I have a external hard drive the computer like to freeze while starting up too( I have a feelig m hard drives about to crash ) and info would help im stuck with parents who now nothing about technology