have a 400 gig h/d with xp pro on it,unregistered version,can get into safe mode but will not let me format it,used my xp disk but comes up with error msg,will not let me install it,how do i get rid off xp pro off h/d?have a hp compaq,about 6yrs old?

Watch the POST screens at start up to verify the BIOS is properly identifying the drive by both model and full capacity. If your version of WinXP doesn't contain at least SP1 then you can't use a hard drive larger than 127/137GB.

i have had the xp version i have on it before,i bought a second hand comp with a xp pro disk,but when i installed it the code was wrong,now i cannot get rid off it and ask me for code or contact microsoft,but i can get into safe mode but it will not let me format?is there a way around it?can i get into c drive and do it?

Read #1 again and do it.