Best Free Security Software Question?

Hello there. I just got my Gateway DX4820 x64-based Windows Vista Home Premium Desktop PC back from some technicians at Future Shop, for a freezing problem I was having & they told my dad that there was too many free anti-virus/spyware/malware software programs, (1 from each category: 1. Avira Anti-virus (Free), 2. Spyware Terminator, (Free) & 3. Malwarebytes, (Free) on there, (which I can confirm that I did download them all) & that they were supposedly clashing with each other, causing the potential freezing & they removed all the free security programs I had downloaded & didn't recommend any free or paid software, that I should try. So, my question to you is: what software programs should I look into purchasing or free trying, that won't cause this freezing problem? Please reply back, with suggestions. Much appreciated. Dan Rocha.