Welcome to the Dell Community  @eversion 

Remove AC, Battery and Base Cover.

Then disconnect the RTC/BIOS battery.

Then connect the AC and try to power-on for just a few seconds.

Let us know what happens???

Best regards,

U2

EDIT: Make sure to push the power button at least 3 times!!!

Thanks. I removed the CMOS battery and plugged power adapter, it BOOTED. I didn't even try to push power button at all. It's turned on after I plugged the power adapter, booted up to last state before hibernate. 

I did try to replace CMOS battery with another one from a DELL latitude e5440 laptop. But didn't try to boot without it. Does the RTC/BIOS battery  (cr2032) provide power to any nvram of BIOS? or just the RTC clock chip? I measured the old battery has 2.1volts, not completely dead. Not sure why it doesn't turn on. Is there any CMOS checksum caused by low voltage?

Can I use the laptop without CMOS battery plugged in? Just with laptop battery plugged in or power adapter. I need to order a new CMOS battery to replace.

Again, thanks for your suggestion.

Wow @eversion that's great!!!!!

This is something that I just recently discovered for this series (E7xxx) of laptop.

I will check in the morning but I think that includes the (E5xxx) series also???

Glad you had a meter to read the voltage of the RTC/BIOS battery.

Not sure why it does this when the battery is low or dying??? "2v and below"

Yes you can run it without the battery but you may need to set the date and time every once in awhile???

I will get back to you in the AM about the (E5xxx) series???

Good work,

U2

@eversion 

Just to confirm that the "E5xxx" series has the same problem.

So your E5440 may show the same symptoms in the future???

Regards,

U2

@eversion 

I can't say for sure exactly what the threshold is but I laid in a good supply of new batteries.

I had stacks of dead "E7xxx" and "E5xxx" series laptops that the warehouse techs rejected.

They would have been sold for scrap/parts.

I saved over half by replacing the RTC/BIOS battery.

Makes me wonder how many we sold for scrap/parts in the past.

Best regards,

U2

I took the CMOS battery out of E7440, and switched with CMOS battery from E5450. E5450 still works with the old battery, E7440 didn't work with either of the batteries. I guess E7440 has a lower threshold of voltage.

Hi

   can you tell me how i fix it. I already face this problem.

Hi 

I also face this issue after removing the CMOS battery it turns on but a certain time this issue comes again and again

Welcome to the Dell Community @chabdulmuqsat 

I to have had that happen.

Make sure the BIOS is up to date.

Dell Latitude E7440 System BIOS:

https://www.dell.com/support/home/us/en/04/drivers/driversdetails?driverid=kdfy1&oscode=wt64a&productcode=latitude-e7440-ultrabook

Let me know if it helps???

Regards,

U2

My Dell latitude e7440 has the lastest bios version A27.