Majorly Slow PC and unable to start programs

Dear Forum,
My PC is incredibly slow at the moment, much more than usual.
Even opening folders takes approx 10-15 seconds.
About a 10 days ago, my (Windows) firewall informed me that my AVG 7.5 (free) antivirus was out of date yet when I ran it, it kept saying things were ok. I uninstalled this, deleted the .exe and files and attempted to download and install a different version of the same program. It seemed to install then instantly uninstall itself again saying it couldnt work. I tried this a few times, same result. (see attachment pics)
I then decided to download and install the free Avast anti virus just to check for any viruses. It installed but wont allow me to run it. It keeps saying C:\Program Files\Alwil.Software\Avast\4\ashAvast.exe is not a valid Win32 application. I have now uninstalled this too.
It has said the same thing for a few app.s lately. My sound has disappeared and although I have installed the realtek drivers, there's still nothing.
Even uninstalling doesnt always work. I tried to uninstall Mozilla but it wont.
I can log online but things are VERY slow. It takes about 90 seconds to open a webpage and an email.
I downloaded CCleaner but it wont open the program and no files appear in the installation folder. (see pic)
It may be worth pointing out that I was using Emule to download from about the time my AVG packed in and I know this P2P has viruses. A virus did show up and I sent the file to the recycle bin. I have uninstalled emule now.
Yeah I know I have been silly using emule in the first place but crying after the event so to speak wont help me lol
Could this just be coincidence that the downloads I downloaded online dont work (perhaps including the SOUNDMAN mixers) or do you think a virus may be in my system prohibiting me installing anything? Hopefully it's not the latter as it seems I cant download any anti virus programs at the moment to even check. :-(
I am using an old PC but it's usually ok. I'm also using Windows Xp serv pk 2
Now I really feel bad...............
Having no sound is driving me totally mad but to think I may now have another even bigger problem just doesn't bear thinking about.
It's looking to me that I yet again am going to have to reformatt a hard drive with many irreplacable files on that I want to keep.
Im beginning to feel like I want to throw my PC away :-\ :-\ :-\
Please help. :cry
Many thanks in advance:
Skinno.
P.S, for the record, also around the same time as things started to go sour, I installed an ethernet adapter on my PC. I'm not sure if this was totally compatable with my motherboard but it seems to be working fine and I dont know if this would affect the functionality of my PC.

 

Hi skinno,
Welcome to the Malware Forum!

What you describes sounds more like a malware than a software problem. Please go to the READ & RUN ME FIRST and scroll down to the bottom. There select the cleaning procedures for your operating system. On the page that opens up, look for the instructions for installing and running Combofix and for installling and running MGTools. See if you can get either or both of these to run and attach the results with your next post, or let us know what happened if you couldn't run either one.

Thanks.
abri