1-go to c:\user\yourname\appdata\roaming\infinitecoin
2-make a copy of the wallet.dat in a safe directory that's your wallet backup
3-remove all other file like blkindex.dat and blk0001.dat infinitecoin.conf... ( dont create another infinitecoin.conf )
4-add again you wallet.dat ( or just don't remove it in the step 3)
5-than start infinite-qt 1.8.5 the new version ( don't use the 1.8 or you will get a bad blockchain)
the qt will download the blockchain and sync