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My friends' desktop PC won't boot, shows nothing on display, confirmed that everything's working fine, but BIOS is corrupted..need to flash the BIOS using bootable CD/USB (Hiren's boot CD or Ultimate boot cd or with similar utilities)

But unfortunately, can't even get into the BIOS to tell the PC to boot from CD or USB drive.

Alternatively, if I remove CMOS battery and re-insert it after some time and restart the PC, will this operation flash/reset the BIOS? so that, no need for bootable cd, and PC can start up.

Shall I try this alternative method? or Is clearing CMOS, not equal to flashing BIOS?

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up vote 2 down vote accepted

Both are Different,

Clearing CMOS means it will just reset to default setting of BIOS or reset to factory setting.

because if you remove the cmos then there will be no power on the board so the password and all the setting will be removed not the bios program.

and flashing the bios means you need re install the bios program.

but go for the second option it may solve you'r problem. (that is try to remove reset by removing battery.)

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Clearing CMOS is not equal to clearing flash.

The settings you have configured like boot order, system time and the like are stored in the CMOS memory. Removing the battery will make this memory clear and the motherboard will revert to its factory settings.

FLASH on the other hand stores the BIOS program. Its contents remain intact even when the battery is removed.

If your issue is being caused by bad settings then a CMOS reset could help, if the issue is in flash then you will have to reflash the BIOS through whatever means are available on your motherboard.

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Clearing CMOS can help if you touched some critical setting and/or made same wrong/non-compliant with normal operating mode. If someone played with BIOS settings it could definitely bring such a problem, like black screen. For instance CPU/bus Frequency and things like that are in scope. The flashing BIOS is useful to upgrade it. If you have already tried to flash BIOS and you were unlucky to have some problems that interrupted this process, for example power failure. Then you have to reflash BIOS, but if so, you cannot now do this from this machine running. Instead, it may lead you to flash it by direct connecting to the SPI connector at the mother board, which involve additional hardware and software.

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In case if you have a Dual BIOS: If you even tried to reflash Bios and it failed it would not be a problem – Ruslan Gerasimov Jun 13 '14 at 6:29

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