still no block source available, 0 blocks processed, now i tried to reinstall  it and crashes every time.

after shut down back to no block avail doesn't show recent transaction.
how do i do formatting
log after restart:
 connection refused (61)
2015-09-23 08:05:02 ERROR: AcceptToMemoryPool: non-final
2015-09-23 08:05:03 receive version message: /Satoshi:0.11.0/: version 70002, blocks=375738, us=82.34.75.229:58532, peer=7
2015-09-23 08:05:03 Added time data, samples 7, offset -164 (-2 minutes)
2015-09-23 08:05:03 nTimeOffset = +0  (+0 minutes)
2015-09-23 08:05:03 ERROR: AcceptToMemoryPool: non-final
2015-09-23 08:05:07 ERROR: AcceptToMemoryPool: non-final
2015-09-23 08:05:09 receive version message: /getaddr.bitnodes.io:0.1/: version 70002, blocks=375737, us=82.34.75.229:8333, peer=8
2015-09-23 08:05:09 Added time data, samples 8, offset +0 (+0 minutes)
2015-09-23 08:05:13 receive version message: /Satoshi:0.9.3/: version 70002, blocks=0, us=82.34.75.229:8333, peer=9
2015-09-23 08:05:13 Added time data, samples 9, offset +0 (+0 minutes)
2015-09-23 08:05:13 nTimeOffset = +0  (+0 minutes)

update:
debug.log 2015-09-23 07:11:16 receive version message: /getaddr.bitnodes.io:0.1/: version 70002, blocks=375735, us=82.34.75.229:8333, peer=36, 2015-09-23 07:12:25 ERROR: AcceptBlockHeader: block is marked invalid 2015-09-23 07:12:25 ERROR: invalid header received 2015-09-23 07:12:25 ProcessMessages(headers, 162003 bytes) FAILED peer=13, lots of 2015-09-23 07:13:07 ERROR: AcceptToMemoryPool: non-final at the end, it does show previous transaction now after replacing wallet.dat with back up, maybe not all lost, still no blocks processed, synchronizing at 13 active nodes

forgive me for my ignorance but how do i "just create it and add the line gmaxwell mentioned"

thank you in advance

hi,
where do i find AppData\Roaming\Bitcoin\. i am running win 8 within mac via vmware fusion 7, when i get to c:/users i olny get to (ticked to show hidden items), i found bitcoin folder in program files but no sign of wallet.dat
thx in advance

i have re-installed it to latest version showing total btc 0.0000, how do i use old back up to get coins back to my wallet?
i get same message 0 out of plus no block source avail, 12 active connections.
thx.

I have backed up wallet, I run os yosemite on macbook pro.

Thanx very much for fast reply, you've mentioned I will have a control of my funds assuming I have the right wallet.dat(how do I make sure of that?)
 

Catching up...Processed 0 of 375438 (estimated blocks)....Last generated block was generated 350 weeks ago.
Qt version 4.8.4.
Used to load very long time until one day I got msg that either main or something block failed to load and now take seconds to load but does not process any blocks still on 0.
Can I back up wallet if I have 0.61188477 unconfirmed coins or will I loose it as unconfirmed.
I would appreciate help or at least to point me in right direction.
i take it simple reinstalling with latest version of Qt will not get my money back? 
Thx in advance.