Boot Problem

Your Hard Drive is getting weak replace it with a new one , sometimes when it gets weak and get bad sectors it does not take up the OS and Boot bcoz the data written get lost so replace it or do the double check as follows

check ur hard drive is it showing u in Bios the main culprit is ur Hard Drive try re loading ur operating system by formatting ur hard drive otherwise Change ur Hard Drive it has become weak , there is a hard drive checking utility like HDDLIFE try connecting it to another desktop and scna it thru this software see the strength of the hard drive ur self download the trial version from website www.binarysense.com and let me know if it helps ,

basically if u computer boots ok and goes in bios when u press key that seems like ur whole pc is working ok incl RAM the only thing that is responsible for the operating sys is Hard disk it is where all files reside so when it crashes or get weak it doesnt give up files to boot so pc is unable to boot forward

pls do vote me if u find me helping and fixya problem