Games missing from steam?

So recently some of the games in my steam library have had trouble running. Half life, for example, failed to launch, so I uninstalled it. Afterwards, it was not in my library and it's steam store page didn't acknowledge that I owned it. Later, Skyrim was doing the same thing, it wouldn't launch, and... show more So recently some of the games in my steam library have had trouble running. Half life, for example, failed to launch, so I uninstalled it. Afterwards, it was not in my library and it's steam store page didn't acknowledge that I owned it. Later, Skyrim was doing the same thing, it wouldn't launch, and the store page asked me to buy it again. So obviously I'm not uninstalling it. This problem has me worried as hell, as I'm not sure what else I'll lose and if I'll ever get back the games I lost. I'm not sure if alot of people are having this problem, maybe the recent summer sale messed something up.
If no one can offer suggestions, please share if you are having similar experiences. (Because unless everyone else has a problem valve isn't going to fix it.)

Ps: I was able to launch the skyrim exe from the steamapps folder.
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