Yeah yeah I know, this is the billionth time I've needed help (what I really need is a new computer).

Here it is; I've just undergone a battle with my stupid computer (and won, for now). So my trial version of AVG 2014 expired and I went to download Malwarebytes so that I have a antivirus program to protect my computer. Well, when I download Malwarebytes my computer entirely freaks out and freezes. So I restart it and then it's even worse; I couldn't access anything on the desktop or open the start menu. So I decide to try starting it in safe mode and after about an hour of trying to get that to work I finally get on and remove Malwarebytes. It's working again now, but now I don't have an antivirus program. I suppose that my computer is too old and stupid to run Malwarebytes, so does anyone know of another antivirus program? It'd be nice if it was free since I really can't afford anything expensive and I'd rather save my money on a new puter anyway. Any suggestions?