vostro 1400 windows 32 bit

i have this vostro 1400 with windows 32 bit. its in the warranty period. while vista was configuring updates i shutdown the laptop. when i started it the next time it wont start. the power light would glow once when i press the power button and then go blank. nothing appeared on the screen completely blank. what exactly could be the problem. conatcted dell support. they send in a technician who figured that the motherboard must be gone. the motherboard was send and changed. but still the system wont power up. so they think that the new motherboard which they sent also must have a problem. so they are going to send in a new motherboard. is the problem with motherboard ??(coz even after changing once nothing changed ..my problem remained...i still didnt see anything on the screen ..the power light would glow once on pressing the power button and then it would go away. ) couldnt it be a softwar problem ?? may be my os or bios is gone ?? what could be the problem??