Q: Can someone help me fix my mac?

A while back, my mac kept getting multiple rapid error codes about my extensions. I found a website that said that if I delete the extensions, the error code would stop. I put them in a folder on my desktop, and the messages stopped. I use my iMac for gaming, and when I went onto Steam, none of my games worked. I restarted my computer, but when it started back up, it got stuck on the white screen with the Apple logo, and white text with a black outline popped up in the top left part of the screen. I talked to an Apple Advisor, and he walked me through redownloading OSX onto my iMac. It seemed to work fine at first, but I soon realized that many things weren't working as they should. Steam wouldn't let me play most games, Google Chrome couldn't access my preferences, and many other things wouldn't work quite right. Whenever I closed a Steam game that would work, it would continually say it was running and I couldn't reopen the game unless I force quit Steam. If I did force quit, however, I wasn't able to open Steam back up unless I restarted my computer, as it said "The application "Steam" can't be opened. -600". If someone could help me fix these errors, I would greatly appreciate it. Thanks.