Cordless vacuum will not power on; battery fuel gauge LEDs flash once then go dark when trigger is pulled.

Safety first: Remove the battery pack before any inspection. Do not short battery terminals.

• Check battery pack: Try a known-good Ryobi ONE+ 18V battery from another tool. If the vacuum powers on, the original battery is likely faulty and should be replaced.
• Inspect battery terminals: Look into the battery receptacle on the vacuum. Clean any dust or corrosion from the metal contacts using a dry brush or cotton swab. Gently straighten any bent terminals with needle-nose pliers.
• Test trigger switch: With battery removed, repeatedly pull the trigger to free any internal debris. If the trigger feels loose or does not click, the switch may be defective and needs replacement.
• Check for obvious wiring damage: Inspect the handle and body for cracks or impact damage that could have broken internal wiring. If you see exposed wires or burn marks, stop and contact a technician.

If the vacuum still will not power on with a known-good battery and clean terminals, the internal wiring harness or control board is likely faulty and should be serviced by a professional.