C:\windows\exe Application not found

Hi

I'm having a number of issues with my PC at present.
I'm using a desktop with Windows XP SP3.

Here is a list of some of my serious problems.

-At first my PC was running very slow.
-Unable to run I.E. since updated to I.E 7. I always got a message about "plugins?" But since I normally use Firefox, it was never a major concern to me.
-Last week whilst downloading some software my ESET anti-virus told me I had attracted a number of trojans.
-These are the notices I rec'd from ESET.
Http://nadsam/temp internet\content\pqz(10.exe
Threat win 32/agent.HTW trojan
IP Address 195.2.253.242:80
NADSAMCABRAN12.com/pqz.exe
etc, etc,.

Since then I came on Major Geeks site and followed your advice on Malware removal. I downloaded and ran CCleaner, de-fragmented my HD's and Installed the anti Malware program.
However, every-time I rebooted my PC I kept on getting a "DEP" pop-up message telling me I had to turn off something in order to run my PC.
This event occurred regularly.
I then as instructed by MG turned on the normal start up using Msconfig.
Since then these are some more of the issues I've encountered.
-PC freezes entire desktop, only mouse is active and my desktop icons disappears.
-I cannot open any programs in either safe mode or normal
-Can no longer use MSconfig or Regedit
-When attempting to open any prog PC asks me "which program do I want to use to open program!"
-I can open or access my email Microsoft Office Outlook
-I can't use system restore
I've noticed some of my personal files appear to be missing, but are there when I view them trough another Admin acc't

Sadly I'm unable to attach any files logs because my pc wont allow me to. I am able to download files to me PC though I'm unable to open them!

Any help would be appreciated.

Thanks in advance

 

Thanks for you assistance in this matter.

Sadly, I can't open System in Control panel. In fact, my only access to the Control Panel is by Right clicking on the CP icon and clicking "explore!":cry

Every time I click on an icon I get a pop-up informing me:

C:\WINDOWS\system32\rundll32.exe
Application not found.

I have tried in safe mode and disconnected my pc from the internet as instructed.

In fact none of my icons will open. Though I'm sure your correct on the DEP problem, if only I could turn it off!

I forgot to mention in my first report, a program called System Security 2009 has found it's way onto my desktop. I've no idea where this has come from.