Your blockchain file got corrupted. Delete blk0001.dat and blkindex.dat from C:\Users\leigh\Appdata\Roaming\Bitcoin and restart Bitcoin and it will re-download the blockchain. Don't worry, your bitcoins are safe as long as you don't delete wallet.dat (which you might want to back up while you're at it).
Awesome that worked thank you so much, very much appreciated
Ive been tearing my hair out trying to work out what was going on