[Resolved]  HP Compaq Presario CQ45 — processing slow

when i recently started my laptop it didnt process and showed an error "BOOTMGR missing" follewed by restart command by pressing "Alt+Ctrl+Del" i restarted it again and the error occured then i conducted various tests and they were sucessfull but still it didnt start. Then i tried to change my "OS" it showed error in hard disk i was adviced to take to hp care centre . Then i again inserted an OS 2005 cd it told to boot the system by pressin Q i did it and the system started working but i still mdont know what is the problem pls advice me for this error in my notebook. Now its working and the battrey back up decreased. I clearly want to know what went wrong.