Make sure the mobo is mounted right on at least 5 pillars ,approx 2mm over case, THERE MUST BE no part of mobo touching metal underneath ,did you plug in psu right,ie some power units ,have 12connector to mobo,plus another 4connector cable from psu to the motherboard.disconnect dvd drive,if using 1ide dvd is set as slave ,ie move jumper to S,slave postion ,rear of dvd.plug in ide ,red ide stripe go,s closest to power cable on the hd.
on some mobos,ram goes in slot 0 first.slots are blue ,yellow,blue,yellow.so for match ram use slot 0 ,blue, and 2nd blue for 2nd.ram chip .IT may be blue white slots on your pc, 1ST ram MUST be in slot o.
ITS not a mistake to buy ide,its cheap,and winxp has ide drivers built in.
IF IDE OR GRApHICS card or ram is loose pc will not boot.
disconnect dvd, try and boot pc ,without dvd ,and hd ,

take antistatic precautions,touch metal watertap.be4 going near pc.
GOOGLE how to build ,assemble a pc.be careful,take it really slow.