That is a good start.....
You need to do the reseating as well if you did not do so. Memory modules, PCIx components, pull and reseat. Or at least rock gently while carefully pressing down.
A bit of evenly coated dust on internal parts is normal to some extent. Static cling so to speak. Of more concern are large scale dust bunnies, hairs, insects, spiders, pieces of paper etc. that block airflow or drag down the fans.
Regarding the PSU - 750 watts correct? Have you kept track of the total power load accumulating via "add new parts"?
Is there a small switch on PSU to select the incoming voltage? Is the switch set correctly? (I am sure that you would be aware of changing the switch but if there are kids around...... Or...