my backups used to work and now they dont.Why?

Hi Im am new to the board but I hope someone out there can help me.I recently bought a DC and acquired some backup games.My kids are a bit heavy handed with the cd's and I was worried they would get damaged and stop working,so I used CloneCd to backup the backups!They worked fine at first but now the self booting ones wont work,although the ones that require a bootdisk still work,and even if I make new backups using the same method as before,they wont work.However they will work if I give the top of the DC a bit of a thump as its booting them up.Obviously I dont want to have to do that everytime I want to play for obvious reasons.The "original" backups still work fine!Has this happened to anyone else? And if so,is there a way to fix it without having to whack the DC each and every time.Cheers,Bob.