Problem in Booting of ASUS MotherBoard A7V266-MX BIOS

I am using ASUS MotherBoard A7V266-MX-UAYZ which has the chipset "VIA
KM266", "VIA VT8235 CE".
My processor is Athlon XP 2400+ . I am using Windows 98 SE as the operating
system.

When I boot the system the follows things happen during POST (Power On Self
Test) :
When I turn on the 'ATX power switch' the "System Power LED" and the "Hard
Disk Activity LED" light up for a while and then both goes off for a few
seconds ( at this time the System turns the power OFF and the CPU fan also
stops rotating ...), then the Systems automatically turns the power ON and
the system boots normally.
The above thing only happens when I switch OFF the "Main power supply" after
shutting down the system, and then switch ON the Main power supply and turn
the ATX power switch ON. It does NOT happen when I do NOT turns the "Main
Power supply" OFF after shutting down the system.

Why does this happen ?
Is it a problem of the hardware/BIOS , or it is a feature of the
hardware/BIOS/POST .
If it is a problem or defect then what is the solution ?

Please help

Regards
Sanjoy
India