I too, am having this problem (no error msg., it just is not working).

I went to mysqladmin, selected ALL and repair. The response was OK in all lists, but the cart still will not show updates of

~ new orders
~ counter stats/last 10 days
~ who's online
~ products viewed

and who knows what else. My host crashed the site in May. They got it up and running ... payments work, I get conformation emails, and the cart counts inventory, but I'm clueless as to how to fix the rest of it. 1.3.9a. Yes, I need to upgrade, but I'm scared to when I don't have a functioning cart now and a possible corrupted DB.