Get a geared road bike if you are developing strength in your knee after blowing it. You will be able to start off in a low gear and keep a nice high cadence as you speed up. Nothing is worse for your knees than trying to transfer to much torque into the pedals. Also you will be able to control your cadence on hills for optimal heart rate.

The number of good used road bikes out there is amazing, and they are cheap, get an alu frame with a carbon fork, and maybe a carbon chainstay if you are lucky.

Here is an example on ebay.

Giant OCR 2.

A million times better than the Windor, a lot lighter too, and just a little bit more money. 2hrs left and no bids at $450.