HEPA
is a type of air purifier. It stands for
high-efficiency particulate air. To qualify as a HEPA filter by government
standards the filter must remove 99.7% of all particles larger than 0.3
micrometers from the air. The following site lists the top 10 HEPA
purifiers available online - http://www.air-purifiers-america.com/AP101_top10.asp.
I would verify that all the parts you removed are properly seated back in their exact locations.
There is undoubtably a safety switch that is not properly closed.
A door, a panel, or a latch that is not properly seated and closing the safety switch is probably the cause.