Whenever I press play, it’d ask me to install although I have done so already.
I’d press install, run ROBLOX, press play, and it’d ask me to install again…
I bet I know whats wrong.
Try restarting your computer and then try again.
Do you have any anti-virus? It was blocking IE and Chrome from seeing I have Roblox installed.
[strike]I’m also experiencing this problem on my laptop.[/strike]
Edit: Restarting fixed it.
I think I should ask this question for you also. 
I restarted my computer, still the same. I turned off Avast, it was erroring
Wait, does that mean turning off Avast fixed it or still not working?
There’s a glitch that happens rarely. Basically, you press play and it never opens, but the roblox client is still running in the background. Killing the process manually don’t always work. That’s why I said to restart.
I turned off avast but the problem is still on-going
Hey supah, did you change your UAC settings recently? I’ve experienced issues after changing UAC while Roblox is installed (particularly when re-installing after changing environments, eg: GT1 to production).
If so, try changing them back to their original setting. If Roblox works after changing your UAC settings back, uninstall Roblox, then revert your UAC changes and reinstall Roblox.
It says this to me 90% of the time but the game runs as expected