Help with windows 2000nt

im tring to repair a dell because windows start up screen will come up then the computer will restart.it will keep restarting till powers turned off...if any knows how to correct with out reformatting please e-mail me at [email protected]..other problem computer has many drives dvd, zip etc..i donot know how to isolate what letter is assigned to hard drive to reformat..i tried a through g and will not let me reformat says improper drive.. help please... also if i use any f8 options windows will just restart and keep restarting