System cannot find system disk during boot.

when i start my pc after tuning power on, the system freezes after displaying the MB logo....and it waits for <tab> 2 enter POST or <del> to enter setup. after i press <tab> it takes much time 4 memory check almost 1 mins after completing that it says that it could not find system disk...but after that if i press the restart switch it boots normally....after boot it always shows my internal hard disk as removeable disk (in the system try)...pls hlp i have assembled the pc just few days ago.


my system config is.
hard disk seagate ST380819AS with firmware - 8.05
BIOS- Phoenix -Award WorkstationBIOS v6.00pg
MB -MSI-K9MM-v with VIA K8M800+VT8237R plus chipset based
Processor AMD Athlon 64 3000+ Socket AM2
RAM 1024MB DDR 2