Help..I cannot get past 2 out of 8 while synching

Question

help, cannot get the full synching to take place  any thoughts?

Answer 1

Dear christ1,
Thank you so much.
But I now believe the problem may have a slightly different basis.
Here is set-up (both PC's run 8.1 and Thunderbird):
a new PC (a)
older PC (b)
both are on the same hardwired router.
While setting up the new (a), Widows offered to bring setting over from (b). I accepted - and it spent several minutes working.
I do not recall if I had already down loaded Thunderbird onto (a) or if it came later. After this (b) Thunderbird shortcut brings up only "would you like a new email address" and "Thunderbird create a new acct".
Thunderbird from the Start Page or the App listings does the same thing.
(b) shows Thunderbird still to be the default.
Now (a) brought down all my old received mail, but none of the sent mail list.
And, important to me, none of the addresses- which were on (b)- they had been moved from an XP outlook express program 2 years ago into Thunderbird.
I have not tried to delete Thunderbird from (b), and start over with it, as I fear loosing my addresses.
So here how you can help me if you have the time.
1. How best can I get (b) to have a working Thunderbird ?
2. How best can I get (a) to continue to work AND have/share the contact-address stuff from (b) as it was before all this.
Thank you again
jim