Did you at least restart inbetween uninstall and reinstall?
Yes I did.
How are the other windows(e.g. Track Motion, Render As) looking like?
They seem to look fine, here’s track motion

Do all event FX windows look like the one in your uploaded image (where there are the tabs Parameters and Custom) or do they vary – like are some of them empty or have other tabs?
They all look like that or appear to.
Check if you have the latest .NET Framework installed (v4.5), if you have previous versions of the .NET Framework (e.g. v2, v3) installed then leave them installed as they might be depended on older apps.
I am having trouble installing one of the security updates for 3.5.1 so I’ll get back to you when I resolve that, but I am up to date otherwise.
When I used an earlier build of Vegas 11, timeline GPU acceleration made my Video Event FX windows empty, so I disabled it and it worked. I highly doubt this, but you might want to try disable GPUA? (Options–>Preferences–>Video(tab)–>GPU Acceleration of video processing(set to OFF))
No luck.