How do I re-instate task manager for XP?

I can't access taxk manager. I believe that Alpha Antivirus has disabled it. I need to get to task manager in order to try to un-install Alpha Antivirus. Please 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.