pressure washer still doesn’t pass water after inspecting check valves. What next?

Check valves look fine. It's industrial pressure washer. 7.5hp, 240v, 3phase motor diesel burner. Previous owner reports ud 10 years, functioned fine then. ideas?
I 3 phase power, electric motor runs fine.
The motor spins, pressure doesn't rise. tried 6 days ago. 5 10 seconds, ruin pump. Today, pump check valves dry, visible internal pumps cd see.

PRESSURE WASHER HOSE 3 8 X 50 GREY
PRESSURE WASHER HOSE 3 8 X 50 GREY
Paypal   US $45.00
Water Jet Power Washer As Seen On TV Hose Waterjet Dirt
Water Jet Power Washer As Seen On TV Hose Waterjet Dirt
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Is a Generac 2250 psi Pressure Washer Good?

I thinking buy ud Generac 2250psi Pressure washer. te pressure washers? 6hp briggs straton engine. Im paying 0 Canadian. curious quality cheap pressure washers.

PRESSURE WASHER HOSE 3 8 X 50 GREY
PRESSURE WASHER HOSE 3 8 X 50 GREY
Paypal   US $45.00
Water Jet Power Washer As Seen On TV Hose Waterjet Dirt
Water Jet Power Washer As Seen On TV Hose Waterjet Dirt
Paypal   US $15.57

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