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How can I tell if the clock battery is bad in a HP Probook 4525s?

My PC does not start when pressing the power button but the caps lock light flashes twice.

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According to the HP Guide for Blank Screen LED Error Codes if your LEDs are indeed blinking twice, then it sounds like you may have a corrupt BIOS.

If the BIOS is corrupt, it may be possible to restore functionality by reflashing the BIOS. This method is not without risk as a bad or interrupted flash may completely brick your machine. You can find more information regarding this process here: HP Updating the BIOS

If you are not comfortable with the above method then there are a couple things you can attempt before that:

  • The first would be attempting a cold boot. Remove the battery and disconnect the laptop from the AC adapter, then hold the power button for around 30 seconds. Restore the battery and try the power button again.

  • Change the CMOS battery. This may be or easy difficult depending on how your manufacturer decided to attach the battery to the system board. Luckily for you, this process is fairly easy for someone with basic hardware knowledge. Page 84 of this document details the process for replacing the battery.

  • Reset the BIOS. This method is useful if you happen to have a bad BIOS set up and can't boot. It is very similar to the above method, but doesn't require replacing the battery. You only need to remove the battery for 30 seconds or so. Place it back in the socket, and try to boot your PC.

If none of the above methods work, it's likely you may need to seek professional, or at least certified help. HP have a number of different ways to get support.

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