Welcome to Bleeping Computer.
Yes, I think you may be on to it, in terms of what may be the cause of your problems. Downloading free things from the internet will get you into trouble almost everytime. You may wish to print these instructions before trying these ideas. For best results, try these ideas in the order written.
It appears there is a program that is starting up, or at least trying to start up, when you boot up the computer and is causing this problem. My guess is that it is the game that was downloaded. Try booting into safe mode by pushing the F8 button during bootup, and then choosing safe mode when prompted. Then go to:
Start > Control Panel > Add/Remove Programs
and see if you can find the program and remove it. Reboot and see if things work well. If not, then reboot into safe mode again and this time go to:
Start > Run
type "msconfig" (without the quotes)
Click on the Startup tab. Here you will find a list of programs that start when you boot your computer. Uncheck the game if it is listed and then reboot normally. If things are still not all right, then repeat and uncheck other unneeded programs, test again. If you are not sure which of these programs are needed and which ones are not, then write them all down and post them here and we can help you. After doing this, is everything ok? If not, reboot into safe mode and try this next:
You could try a system restore to restore your settings back to the way they were before, back when things worked right. More info on this can be found HERE
Lastly, if you cannot boot into safe mode let us know. Write down exactly what happens, and error messages you get, if any. Also please document everything you do, and report back.
Oh, one more note. This game was probably bundled with some malicious software, as many of these types of malicious programs use the .net framework to install themselves on your computer, or at a minumum encourage you to install the .net framework to make their job of infecting you easier in the future.