Computer can not boot with any disk of vista n 7

Hello,
every one PLS HELP ME i hv my 'hp compaq dv6720' laptop.i got 'Vista business' preinstalled in it. It was not responding alot, so i tried to change OS to win7, i execueted .exe file from a iso file put in my pd. Every thing gone well, after showing dat 'ur computer preparing desktop for first use' it restarted automaticly n, just paused no a BLACK SCREEN WITH WHITE CURSOR , i tried to boot it with ubuntu, and i done, but if now i'm trying to boot it from my original vista or other window 7 disk den it even not detecting disk n jst the same problem of black screen n cursor...coming i tried to boot it with WINDOW98 cd den it verified disk 2times. But nothing happenig so that i can start any window. Only jst black screen is coming... PLS Help WHAT SHOULD I DO NOW, pls reply any possible ans. Email Id removed for your security" pls pls pls... I'll not forget dis favor on me:)