My Rollercoaster Tycoon 3 doesn't work?

I have the Disc and Steam Version. The game works but lags so badly it is unbearable. I think it started happening when I got Windows 8.1. It worked f

I have the Disc and Steam Version. The game works but lags so badly it is unbearable. I think it started happening when I got Windows 8.1. It worked fine before. I even tried deleting ATON of hard drive. Any suggestions?

or:I have the Disc and Steam Version. The game works but lags so badly it is unbearable. I think it started happening when I got Windows 8.1. It worked fine before. I even tried deleting ATON of hard drive. Any suggestions?

or:Try formatting your drive C: and installing earlier version of windows

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