Switch off the desktop (if on) and switch off and disconnect the power from the desktop
Find the coin cell battery located on the motherboard and remove it from the motherboard. Remember the orientation of the battery for when to go to put it back in. (usually +ve on top)
Whilst it is out measure its’ voltage. Usually coin cell batteries are 3V DC, non rechargeable and last for 5-7 years. If it is less than 2.6V DC replace it. The type is usually marked on the battery (CR2032 perhaps)
With the coin cell battery still out, press and hold the desktop’s Power On button for 30 seconds and release.
Re-install the coin cell battery (or a replacement) reconnect the power to the desktop and try to turn on the desktop.
If the desktop starts you will probably get a message about the Date and Time being incorrect so you will have to enter BIOS and set the date / time etc.
Once it has started OK check what happens when it has gone into sleep mode and you want to wake it up or if you turn it off in the normal way and then try to start it again inthe normal manner."
