After clean install of winXP old problems appear again..

After using files from p2p networks I noticed a decrease of my PC performance and some evident problems.The first is that I can't use operating system evaluations on virtual machine (VM-ware player 8) because they all don't work properly(windows xp/7/8).The player itself has problems with starting an OS (dialog boxes that appear to inform me about devices that will start connected or not,are frozen about 10-20 seconds.If you know well vm-player there is a posibility to change VM settings.Changing those settings on my PC causes a total unresponsiveness of the PC(even alt-ctrl-del doesn't work).At that point the only thing is restarting the PC.2:When I play time dependent online-quizzes there is a constant delay after answering so I can't obtain good results even I respond correctly.3:When running video or audio internet streams there is a drastic sequence irregularity(video) and some kind of constant noise,rustle call it whatever you want(audio) so services like youtube,sport event trasmissions or radiostations are practically useless.I went to several pc-tehnicians many times paid them for a,it seems not well done work because right the same problems reappeared after a little period of time.I tried even a clean install of XP and 7(downloaded from microsoft) myself.Then I didn't connect internet for 1 week and all worked well, even VM but,a short while I installed wireless adapter driver and connect to internet I gained all those problems.Now,I know something hides itself in hdd somehow and after getting the posibility to contact its server over internet downloads and executes 'naughty' files on my machine.Without internet this thing is harmless.Now the thing is if there is someone who can help really.That's why I am posting.