windows 7 - Is clearing CMOS and flashing BIOS same operation?
2014-07
ISAAC
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?
ali786
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.)
Ruslan Gerasimov
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.
VBwhatnow
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.
ianfuture
Motherboard is : ASUS A7N8X-E Deluxe, Rev1.01,
On start up get: "cmos checksum error - defaults loaded" error BIOS is reset everytime and can't boot to Windows off HDD.
POST report is ok once I tell it there is no Floppy drive attached and not to seek it. The boot sequence starts then just as get to load windows safe mode options whole PC shuts down. BIOS is reset to defaults again.
I've checked the battery and jumpers. Tried a known working battery. Changed Graphics card, changed memory, changed HD to one without an OS. Disconnected DVD drive. PSU is known to be ok.
IN BIOS CPU is recognised correctly and memory is also recognised ok.
So is it likely to be a bad motherboard or corrupted BIOS or something else?
Thanks :)
hanleyp
From your description, it sounds like this happens every time you boot.
- Do you only boot your system by switching on the AC power to it?
- Does this also occur after you power down from the OS or by pressing your power button for > 4 seconds causing the system to go into "Soft Off" or ACPI S5 mode?
- Is the time reset each time you have invalid CMOS checksum?
The reason I'm asking is because the VBAT power connection is typically powered by an on board regulator when the system is plugged in and by the battery when the system is disconnected from the AC outlet. You can measure the VBAT voltage and if it is ~3V or less then it is running off the battery, but if it is closer to 3.3V, then it is powered by the 3.3V DC-DC regulator on the motherboard.
If #1 above is the case, then it is likely the battery connection. #2 is more cause for concern that the motherboard isn't behaving as designed.
There is a third potential problem. Some motherboards have a Clear CMOS input which does not GND the path from the battery to the VBAT power input. Instead, when asserted, it clears the CMOS, but not the time. Look for a header with this connection to make sure it isn't shorted.
Also, bad electrolytic capacitors being the cause is unlikely because the VBAT connection is a low current connection and any capacitors on it are not likely to be electrolytic. The 3.3V voltage rail may have capacitors, but even if the voltage dipped, the VBAT power usually can go as low as 2.6V without CMOS corruption.
William Hilsum
Obviously impossible to say 100% without seeing it, however, I had one of these last week that was very similar (also on a Asus motherboard...).
I tried reflashing BIOS but go nowhere, I attributed it to a bad motherboard and got a replacement under RMA.
ianfuture
After all that and lots of fiddling it appears the CPU was overclocked in BIOS and had become unstable. Only by chance I noticed this. Thanks for help :)
8088
Dude, that is an old board. I remembered I had it like 4 or 5 years back. Check for capacitor leaks or any forms of burnish on the board - they might be causing those errors.
It could even be that the wiring paths from the batteries have corroded somehow. It's 5 years, time to give it a rest.