Again, because 3.5 is bundled with Windows 7 (read my post above). 2.0 is not bundled, so if you installed it separately it will list in your Programs. Best to use the verified program I linked above to enumerate and test the versions you have installed.
.Net framework can be a messy beast if it gets corrupted. In order to fix it you often need to remove every version you have using a variety of means and then reinstall. This can sometimes break other programs as well. The good news is that I rarely see a system that requires this (maybe less than .05%).
The blog site that the verifier tool is on above has resources for fixing .Net.
I don't know your full issue, but just because you are not seeing something listed doesn't mean it isn't there or is broken. Run the verifier tool and if it shows that your .NET is ok then start looking elsewhere.
More info on .NET Versions
Unified .NET Framework Troubleshooting Guide
Additional .NET troubleshooting steps
.NET cleanup tool