Note: No hardware problem will take you till welcome screen ! (very less chances)
If you dont have Win7 disc, atleast vista or atleast XP.
Insert it --> Boot via cd--> during installation menu popup press "Shift+F10" or some system "Shift+F8" this will take you to Command prompt. Try anything that will bring CMD prompt. After poping up of CMD
Type: BOOTREC.EXE, now follow the repair instruction. there are more ways to bring CMD which is more powerfull command in Windows.
Important: Never FORMAT hard drive in any circumstance, unless it must.
Good luck