My computer has been taken over by viruses. My anti virus does not remove viruses and any new anti virus I download becomes infected. Need help.

May be your computer is at high risk, because when you install any antivirus or any other programme it is infected. This means that virus and its infections are very high in your computer. If you insert any USB drive or any external drive, virus might damage your data. Before doing all these if you have any important data take a backup of them.

After taking backup of data, format your OS drive or C drive, After doing the same you need to check with other drives. But I assure you that other drivers like D, E ...etc are also infected. After formatting and loading the OS you need to install the Internet Security, why I am saying Internet Security means it has all the features like spyware, Malware  root kits  virus protection...etc. If you want you can try trial version of Norton Internet Security for 30 days.

After formatting and installing OS dont install any drivers or any other software's  Just install the Internet Security programme. Update the virus definitions  and scan the whole computer. I assure you it detects and removes threats, if that feels good buy full version of the software.

But every time install a security software's  don't overcome that my pc never gets virus or I am sure my USB drive does not infected with virus. Any way so many antivirus programmes are available on Internet, Free version of antivirus is Avast that was good enough to protect your PC. 

I got norton first and it was working great but my subsricption is running out so yesterday I added avast free antivirus and it's kinda slowing my computer down a bit.

 Sol :- It is not safe for PC to have two antiviruses, one PC should have one Antivirus  with regular updates.

An Antivirus programme is mandatory, because now a days tonnes of viruses effecting th operating sytems. Some company's provides the antivirus programmes free version.

If you cant afford to buy one try Avast, Avira. Avast is good antivirus it detects and cleans viruses, but it is limited programmes not works in depth and Avast provides regular updates with one year license to it's users.

If any PC installed with two antiviruses, two programmes fight against each other. PC processing will become very slow and the work is totally time consuming. 

In a full version, they give so many features such as updates, upgrades, live support, technical support.