I found an old PC (Progen) in trash that didn't come with hard drive and CD-Rom, but when first try to startup it can go to BIOS. (it has about 32 MB RAM)
Because BIOS has password protected, I try to reset the password by removing CMOS battery and wait for about 24 hours then install back the battery.
The problem now the PC can't go through BIOS, the fan is spinning and green light is on but no beep sound.
Don't know if the battery problem or the mobo already dead
Thanks for any help

CMOS only retains BIOS settings for a few seconds after the battery is removed. 24 hours is just insane overkill.

Also, on most semi-modern machines, the password isn't stored in volatile memory and as such will never be "reset" using that method - There will be a jumper on the motherboard to specifically erase the password. You should search for that motherboard on the internet and fine the manual for it.

As for the machine not POST'ing anymore, I would suggest that you moved a jumper or that something is not seated right. Double-check that the ram, cpu, video card, any other peripherals, cables, and battery are all seated properly. If in doubt, remove them and re-seat them. Find the manual for that motherboard online and go through it, checking all the jumpers on the motherboard to make sure they are in the correct positions.

Also, that battery may have died in the meantime.

Finally got it, just change the new battery, and everything is working now, and no more BIOS password.

For how long you have to remove the CMOS battery, I think it depend on your mobo, some people suggest 10 second, but some said couples minutes, even several hours or more extreme until several days.

Thank anyway pal for your help. :grinthumb