I can offer advice that may be causing the issue, but the best advice will come from the Hypertherm tech service staff. The call is free, and they spend their days talking with Hypertherm systems users, and likely will be able to walk you through the issues.
Contact info: Technical Service
800-643-9878 Tel - Toll Free in USA
Here are a few things that can affect starting of a blowback style torch:
1. Electrode and nozzle....have you replaced these?
2. Retaining cap may be overtightened....it only should be snug.
3. Swirl ring...over time these can wear out, which will impede starting. Replace.
4, Retaining cap could need replacement.
5. Inlet air pressure too high. Turn Amps knob fully ccw, adjust air regulator while air is flowing using LED pressure indicator on front panel.
6. If a lot of moisture got in the torch...the torch plunger assembly may need to be disassembled and cleaned. Refer to the Powermax45 Service manual for detailed instructions. Service manual can be downloaded from Hypertherm | Plasma Cutters | Plasma Cutting Equipment | Metal Cutting Equipment, click on document downloads, choose the Powermax45, scroll down to service manual and it will download as a .pdf.
7. Make sure you are using Hyperther genuine parts. Aftermarket consumables have stack up tolerance issues which can cause misfiring.