Windows security alert along with anti virus pro warning

I have a dell dimension 4400 running windows xp home ed and I just got a security pop up warning message that will not allow me to open task mngr nor will it allow me to open Hijack this, will not allow me to open any anti virus software. Only in safe mode will it allow me to scan with avg 9 yet it will not fix this problem. The windows security alert states application cannot be executed then it tells of the file that I am trying to open is infected yet it does that with any file or program I click on? I do not want to have to do re installation of windows and am hoping that you guys can help...

Please download the current version of HijackThis from HERE

• Double click and run the installer.
  
• It will install to C:\Program Files\Trend Micro\HijackThis\hijackthis.exe
  
• After installing, you should get the user agreement, press accept and Hijack This will run.
  
• Select Do a system scan and save a log file. This will open a notepad file of everything Hijack This found, copy and paste it back here.
  

I noticed that upon restart of windows xp That I could get avg to run after 3 scans I was able to get rid of it!!! It has been doing great since and have been really thankfull for your help maybe next time I will actually get to use it!!! javascript:emoticonp('')Once again thank you!