Is Avast free virus good enough to get rid of any kind of Virus and other for a Laptop?

After running Avast freeware I found no Virus on computer or anything. Seems like once a month though the computer acts up and I have to redo everything. Can a Virus or anything like that be in a computer but not on or in the hard drive? Can a Virus or whatever be in the Bios?

Avast free antivirus, has the limited features, which I have observed alot. In a situation the avast antivirus not detected any virus. After I uninstalled the Avast and Installed the Norton Antivirus Trial. Updated virus definitions, Scanned the whole computer and shocked by seeing the scanned results. It had detected about 150 infected files (tojans/viruses/rootkits). 

As there are many infected files, I am thinking that why Avast did not. I checked the features that which provided by the Avast and compared with Norton Antivirus features. It's totally different. We need to check the details and features of the programme before buying or downloading.

Avast can also detect all these infections. but you need to Buy the Full version. Check the picture below.

If you buy the Avast 7 Internet Security, It will detects the virus/trojans/rootkits. If you can afford you can buy