alpha antivirus

i was just on my computer n this thing popped up sayin i had a virus n to download it n i did but that was the viruss can i have some helpp please? thank u so much! and theres been 45 threats n it just almost crashed i think!! helpp quick!!!!!!!!!!!!!!!!!!!!

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.