automatic wallet.dat I installed a bitcoin-qt  and received a transaction. Few minutes later, the pc crashed,after restoration of the pc,I only saw  an automatic saved wallet.dat file  I tried to recover fund but no avail. Please help me to restore my fund
Bitcoin core has keypool option enabled by default, so when you install it a %n of keys will be generated and saved on your PC so when you generate Bitcoin address the address is coming from keypool which is already saved on your PC.

So, Your bitcoins should be on your PC, just give it some time to reindex. 

and check debug.log file.