computer slowing down/crashing - no malware

I get that pop up that says windows has detected high memory ussage and a number like 343 or 405 Mb and to close and re-open the application ( interent explorer ). also when I watch movies online or even now youtube the computer will sometimes slow down and move thru a function very slowly. that is to say that if I hit one or two keys too quickly the computer freezes and will sometimes stop in mid frame or it says tab recovered, and the page will reset itself.

I have downloaded and un-installed several utilites repair programs which are fine to scan and give me a diagnostic but they want money to repair the problem. so I have a list of things here that they said is wrong.

1 : my PC stability is poor - top crashes - windows re-start manager / register server / windows capi2 // size of hard-drives - 159 gig - it should be 250 ( this a reimage scan )

2 : system service status - dangerous / personal privacy traces - 86 / usb autoplay status - dangerous / network settings not optimized / junk files - 3248 / registry redundancy - 17 / windows boot time 109 seconds - should be 90 ( 360 scan ).

the other thing is that someone said I may have too many applications or programs RUNNING that dont need to be, but I dont know which ones should and should not.

my question is which downloads that are free can I use to repair these problems or what can I do on my own computer to correct what is wrong?

 

First what version of Windows with Service Packs are you running?
Second how much RAM is in the computer?
Third give the make and model of computer.