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Steve Simpkin · (This post was last modified: 08-14-2022 01:50 AM by Steve Simpkin.)

Try the following in order.

1. Verify the batteries are installed correctly.
2. Try the reset or memory clear methods on page 217 and 218 of the manual.
3. Remove the batteries and short the contacts in the battery compartment for 10 seconds. Put the batteries back in. If it is still unresponsive, repeat step 2.
4. With the batteries installed, short the contacts for less than 1 second. This brief short won’t hurt the batteries but may jolt the calculator back to life. This is from the HP-15C manual.
5. Apply pressure on the bezel between the top row of buttons and the LCD and try the ON button.
6. Try another set of batteries in case one of the ones you have has a high internal resistance.