Webpages won't render

Hi guys, I have a problem I hadn't come across before.
Everytime I go to any website, the graphics are no displayed properly and the pages themselves don't look ok.
for example, a website may have five or six jpeg images and five will display properly but one won't, or often when I go to any webpage, all I can see is the source code and when I hit refresh the page, will display although with errors, I can iether see only source code or a mix of rendered page and source code, all downloads seem to be corrupted so I haven't been able run anti spyware programs and I can't access asus website.
All jpeg images in my hard drive display properly and all the videos seem to play ok, so I think that has to be the way that the machine access the net.
Since the problem started I have installed the OS in a new hard drive so hard drive or os is out of the question.
Is it posible that the mobo is playing up somehow?
I was running this set up, no faults for a month before the problem started.
The one thing I did before the problem started was to donload some codecs to watch a movie ( the movie is an original DVD region 2) but as I said before I have reistalled the OS since.
I have tried donwloading sisoft sandra in another machine and then install in the one with the problem but it won't install, same goes for avast, zona alarm and spybot S&D.
There's no other problems I am aware of, except webpage rendering and failing to install some programs.
Specs as follow.
Asus A8N-SLI Deluxe
Opteron 64 175 dual core
OS tried in 3 different HDD, a Barracuda ATA 120gb, a samsung SATA 200gb and a hitachi ATA 80gb
ATI Radeon x1900xt, Tried latest Drivers and the ones that came in the CD
I have a DVD PLayer and a Burner but I have unpluged everything except for the power for the gfx card, one HDD and the fans
Thermaltec 500w and a OEM 450w, have tried both.

I will apprecciate any sugestions, specially if someone has come accross something like this before.
Thanks all.
I don't know if I can post links yet but I can take some screen shots if anyone needs to see how things look.

So, basically you can't install any computer cleaning product and the problem perists over a reinstall of the OS?

To put it blunted, you're fubared thanks to some nasty peice of software in that codec pack you stole, sorry, downloaded for free...

My recomendation is as follows

1) Purchase new HDD
2) Remove old HDD from your computer.
3) Do a full CMOS clear, then reflash your BIOS.
4) Destroy old HDD completely, do not put it into any other machine just in case :)
5) Reinstall OS and before you connect to your home network or internet connection, make sure you have an anti-virus, anti spyware and firewall installed.
6) Stop trying to get free pieces of software and pay for them!!

Really helpful advice that.

You definitely have some malware, I'm guessing a Trojan. Your PC is quite possibly being used as a spambot or for some other nefarious practise every time you're online, which is all the time if you have broadband.

These programs are memory resident as well as being infecting drives, so unless you did a clean install on a new HDD without the old HDD or its data then it's probable that you just transferred the infection.

Most AVs, including the free ones, catch 99.9% of attempted infections, but they can't stop user error - I've seen people override them, sometimes accidentally because they didn't read the popup, and install the malware anyway.

You have three possible course of action that will probably work.

1. Delete the existing HDD partition and set up a new one. Rather extreme as it will also destroy your data, but works against any malware I'm aware of.
2. Try booting from another drive: DVD/CD/flash or floppy that is write-protected and contains malware removal tools - you will need to download these on another computer and create the bootup disk.
3. Try looking in task manager and spotting rogue programs running. You can then search these out online and find out how they can be removed. You will probably have to reboot in Safe Mode and not load drivers to get a clean removal. This is the easiest solution, and I have managed this half a dozen times on other people's infected PCs, but does require a fair bit of Windows expertise to manage properly.

Thanks Thorsson, I did erase the hard drive with Darik's disk eraser and then partitioned it with Ranish after that failed I installed the OS in a new HDD without the old HDD installed, I have already cleared the CMOS and removed the memory and reinstall it (as far as I am aware of memory don't keep data once its not being electrically fed), but you gave me an Idea and I will try to run Hijackthis from usb, I will let you know what happens.
Lucio, you are true to your statement that you have nothing good to say, so you should keep your trap shut, you are showing complete disrespect agains a person who you don't even know and you show complete ignorance of how codecs are made available to people, yes there's people that take advantage of freeware to distribute nasty things on them but there's as well loads of free software that does the job perfectly, if you pay for microsoft office, photoshop elements, audio editing programs anti spyware, antivirus, firewall, etc. you are a fool because there's perfectly good and clean free programs to do that work.
Do you have any idea what GNU GPL is?, do you know what DivX is?
Have you heard of Avast, Zone Alarm, Spybot S&D, 7zip, The Gimp, Audacity, Open Office, Firefox, Thunderbird, virtualDub and DVD flick?
If you haven't, then just do a quick google, you will be surprised.
Sorry everyone else, I am usually no bother with this kind of crap but it pisses me off that someone is acusing me of stealing something that I did not steal.
btw, I know for a fact that at some point every single one has downloaded something you shouldn't, and if I look in Lucio's pc right now, I will find something that has not been paid for.

Perhaps you have a BIOS virus. Have you tried re-flashing the BIOS? You would obviously have to do this in conjunction with wiping the HDD again.

see if you can find a virus/spyware scanner that can run off a memory stick