Antivirus software alert:Infiltration alert. Antivirus Live

My netbook is not usable. This thing took over everything. I can't use anything on the computer except the internet and in IE it won't let me even go to google. I can download in Firefox but can't run anything. I can't go into safe mode either I can't use my antivirus I have installed. I can't run hijack this. I can't open hijack this or anything else. I can't go into add/remove programs at all. Porn keeps popping up too. Websites are porn.com and porn.org. I don't watch porn online. I have no idea what I have been using that could have given me this. I NEED HELP!!!!! WHAT CAN I DO? I am gonna get an online website in 2 days and I can't do anything without my computer.

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 already said that you can't open or run anything. I also mentioned that I downloaded hijack this yesterday. It is downloaded but gets stopped. It says "Application cannot be executed. The file msiexec.exe is infected. Do you want to activate your antivirus software now?" I has basically assumed that everything on my computer is a virus and stops me from being able to open it. As soon as the pc comes on I have gotten to start my antivirus but only for a few seconds. When it starts the computer gets mad and turns itself off immediately.