Classic Outlook Keeps "Not Responding" and freezing

Hi Brittany, thanks for the replies! My answers in dashes --

OST files for 2 of the 3 email accounts are around 3,500,000 KB the third that is not used often is only 65 KB - Could this be the issue -

--That's not too much, 3.5 gigs. Should be ok!

my smaller account is not having as many issues.

--Noted
the AOL accounts are running fine

--Noted
I've had my antivirus - with no changes on my part/company's part for over a year, is this still something worth looking in to?

--Probably not if there are no changes

Windows and CO all updated/current

--Noted

Notes to make that I found after posting - When sending test emails between my small OST file account and the two largers. When I didn't attach our signatures it seemed to work much better. - not perfect but better. Could html be the cause of this in any way? 

--Possibly, does the signature have a lot of links in it or a bad image? Try using a Text signature and see if that works better. If it does, check the signatures and verify the links and images of size, could be part of the problem