What Does This Error Mean?

An HP calculator that will not turn on is almost always caused by a flat or deeply discharged battery. Replace the battery with a fresh one. For the HP Prime (rechargeable), charge it via USB for at least 30 minutes before pressing the On button — a completely flat Li-ion battery will not respond immediately.

Affected Models

HP 12C
HP 17bII+
HP 35s
HP 50g
HP Prime G1
HP Prime G2

Common Causes

Battery flat or completely discharged
HP Prime deeply discharged — requires extended charging before responding
Battery contacts corroded preventing electrical connection
Reset button accidentally pressed — calculator entered a power-off reset state
Internal fuse blown from battery reversal (rare)

How to Fix It

Replace the battery.

For calculators using coin cells (CR2032) or AAA batteries, replace all batteries with fresh ones. Ensure the polarity is correct — positive (+) facing as marked in the compartment. For the HP 12C, the battery is a single 3V coin cell under the back cover.
For HP Prime: charge via USB before pressing On.

If the HP Prime's Li-ion battery is completely discharged, the screen will show nothing when you press On. Connect the HP Prime to a wall charger (not a PC USB port) using the included USB cable. Leave it charging for 30–45 minutes before pressing On. A fully dead Li-ion battery takes time to reach the minimum activation voltage.
Perform a hard reset.

Locate the reset pinhole on the back of the HP calculator. Insert a straightened paper clip and press the reset button for 3 seconds. Release and try pressing On. A hard reset can recover a calculator stuck in a deep sleep or error state.
Check battery contact cleanliness.

Open the battery compartment and check the spring contacts for corrosion (white or green residue). Clean contacts with a cotton swab dampened with isopropyl alcohol. Dry fully before reinserting a new battery. Corrosion is common on HP calculators stored in humid environments.
Try a three-key reset (HP 50g).

On the HP 50g, hold the On key, C key, and the left arrow key simultaneously for 5 seconds. Release and press On. This performs a deep reset that recovers the HP 50g from a complete non-responsive state.

When to Call a Professional

If fresh batteries and a hard reset produce no response at all — no screen, no key response — the main PCB or power regulation circuit has failed and the calculator needs professional service or replacement.