Windows booting problem

Hello,
hello sir,
I am using Pentium D processor system wih a ram of 1.5 GB and motherboard 946GTZ. I am having a problem in booting. When ever i open my system it will not open that means system will boot first it will do POSt after that when it comes to first boot priority if it is hard disk, it will try to open windows but unable to open and at lastcome to network boot and stop. I am windows xp with sp3 OS in my system. When gives first priority as cdrom it will boot OS cd and dislays message "press any key to continue" which is common in every bootable cd's. When i ignore this message and not pressing any key durrying this message, it will automatically starts booting my hard disk and starts windows normally.

Please help me.

Motherboard: 946GTZ
Processor: Dual core 2.6GHz
RAM: 1.5 GB
Hard Disk : Seagate 160 GB newly replaced
CD Drive: Combo Drive Samsung