Did you get a reply about this problem? I have the same problem with my two month old 10W A5 engraver. The fan is on but no laser. I have only done a few small wood jobs. I have already had to replace a stepper motor and can't justify buying a replacement laser that costs 3/4 of what the machine was worth to start with.
I'm very sad about this. My friends are getting married and we had plans to make them some personailised coathangers for their day.
I took the machine apart yesterday and the left hand extrusion was a bit rough along the rails. So I went over with a bit of wire wool. I also put the belt fastnersI found on thingiverse at https://www.thingiverse.com/thing:2564431
These helped me tighten the belts again with the same tension each side.
All is now working great and I am getting some really good engraving results.
Thanks for the help.