I would suggest downgrading your DM to version 4.7 to start. Choose it from the list here: https://www.blackberry.com/Downloads...93E4F3BB068C22
Lots of folks report bugginess with 5.0, and a downgrade clears up a lot of it. Stick with the version without media manager too as that's just one more thing that drives folks nuts with issues.
On your BlackBerry, go into Options > Memory and ensure: Media Card Support: On
Encryption Mode: None
Media Transfer Protocol (MTP): On
Mass Storage Mode Support: On
Auto Enable Mass Storage Mode When Connected: Prompt
These are my settings on my Tour and I have no trouble connecting. Your 8310 may not have all these options, but match as many as you have.
Be aware that if you're on a BES system from work, an IT Policy may prevent local syncing. In that case, there's nothing for it but to not sync. Likewise, if you bought this BlackBerry used, it may have an old IT Policy on it from the previous user, and this policy would still be in effect, preventing you from syncing locally. Remove IT Policy - BlackBerryFAQ