So for the last few months, I noticed the little hood release plastic lever was a bit loose on the left side of the dash. So today I go to open the hood, and it makes the pop sound but won't open. The plastic was a bit more loose, and the lever can almost come out.

What can be wrong here? Did something let go? Any other way to manually open the hood?

 

If there is tension on the hood release lever(it must feel tight if normal) then there is your problem. Try having someone push down slightly on the hood on both sides while you pull the lever to see if it opens, if not check tension on the cables to see if anything has come loose.