Upon finishing the first quest for Brynjolf in Riften involving lockpicking a box to plant the ring on an NPC (can't remember the name), he tells me to talk to him in the Flagon Dragon. He doesn't give me the quest he should have, though, called "Taking Care of Business". I was unaware of it at the time, so I cleared out The Ratway and made my way to the Flagon Dragon anyway. Brynjolf wasn't there, so I figured I had to wait until night time. I did. He showed up, but when I tried talking to him, he just replied, "Hmm?"

I reloaded to an earlier save point to try the quest again. I did it perfectly, he still didn't give me the quest. My friend told me that getting an Unusual Gem and showing it to Maul would prompt me to talk to Brynjolf and get the quest also. I got an Unusual Gem, talked to Maul, he told me to talk to Brynjolf, but I only got the same response from him. "Hmm?" After this failed as well, I cleared my system cache. No dice. I tried installing it to my hard drive (I play on X360), nothing. This is really bumming me out because I was so excited to start the Thieve's Guild quest chain.

Is there anything I could be doing wrong that won't allow me to get the quest, or any alternative to joining the Thieve's Guild? Help PLEASE.

that is odd; i am in the thieves guild from doing the quest you described, and i dont think theres another way to get in. Sorry to hear about this :[

So would the only solution be to ask for another copy? Or continue with the game and hope a patch comes out to fix this..

After the 1st quest where you pick the lock and plant it on the other guy, I had to meet Brynjolf in the inn first, then I got the quest to meet him in the Ratway.

Which inn?

Bee and Barb