Problem with computer

Ok I've tried to reformat my C:drive to see if i could delete my D: partition but it didn't work everytime i tried to boot my compter to start with windows xp pro setup it wouldn't boot up from it so it would always try to boot C: but it couldnt so it said "invalid system disk". I restarted it many times and then finally I took out my hard drive and put it back in my friend told me to do it ( i found out he was drinking when he was talking to me.) so now i hooked it back up and it wont turn on anymore it flashes green for a little and then will go to red and keep flashing. what do i do now get another hard drive or just get another computer or some other parts for it?

 

the computer was off when you took it out right? if so make sure it hooked up right and make sure that the power is hooked up good too.

 

It was off its done this before when it i put it into stand by mode but it didnt last for this for 4 days i keep trying to see if its hooked up because there are 3 wires so i keep puting easch in there butit doesnt work it just keeps flashing red.

 

also there was this button on the motherboard i think and i pressed it and my computer tries to start by itself but it wont fully start up it will have the green like for like 8 seconds and the fan but then it will go to flashing red again i dunno what it is if someone could help me with that i could probably
try to fix the xp error.