Antivirus System Pro or Platinum

Is anyone familiar with this? We know little more than the basics about computers and probably made a huge mistake.

We have had Trend Micro for years. Last week several times when we got on the computer, the virus protection would be turned off and we would have to manually turn it on. Saturday morning, our computer was obviously highjacked. According to the Antivirus System (we don't know how it got on the computer) we had 34 viruses. We could do nothing... could not connect to the internet, open any files, play games, etc, except for the Antivirus System Pro or the Trend Micro window. On the Trend Micro window was the same emblem as the one on the Antivirus Systen Pro window, so we thought, okay it's the same company and we knew Trend Micro was due to expire in a couple of weeks. When we clicked on the "buy now" button on Antivirus System, it immediately connected to the internet and let us purchase lifetime protection for $69.95 on our credit card. Also immediately, there were no more problems connecting to the internet or opening any of our files.

Now it appears that Trend Micro and Antivirus System are battling over control of the computer. Antivirus wants to change settings and Trend Micro opens a window, asking if we want to allow the changes. What should we do?