user27983: I wanted to back up the blockchain on my hard drive as it took around 50 GB on my laptop. I did so and deleted all the blk000.dat and the rev000.dat from (~/Library/Application Support/Bitcoin/) which are saved on my hard drive. Apparently this was a stupid mistake as I cannot open Bitcoin QT anymore. I therefore re-transfered everything back to the same folder. But nothing happens, and Bitcoin Core does not open. 
After looking around, many are mentioning a bootstrap.dat file which correspond to the block chain. I cannot seem to find this file anywhere on my laptop.
Any clues? thanks a lot!

user3697: Delete your chainstate and blocks folder and start Bitcoin-Qt again. It will then re-sync your blockchain.

27983: <p>I wanted to back up the blockchain on my hard drive as it took around 50 GB on my laptop. I did so and deleted all the <code>blk000.dat</code> and the <code>rev000.dat</code> from (<code>~/Library/Application Support/Bitcoin/</code>) which are saved on my hard drive. Apparently this was a stupid mistake as I cannot open Bitcoin QT anymore. I therefore re-transfered everything back to the same folder. But nothing happens, and Bitcoin Core does not open. </p>

<p>After looking around, many are mentioning a <code>bootstrap.dat</code> file which correspond to the block chain. I cannot seem to find this file anywhere on my laptop.</p>

<p>Any clues? thanks a lot!</p>
 3697: <p>Delete your <code>chainstate</code> and <code>blocks</code> folder and start Bitcoin-Qt again. It will then re-sync your blockchain.</p>
