Not sure how much you weigh but sometimes when it’s cold the seat Safety switch won’t depress. Does putting you knee into the seat help?
This, of course, is assuming you have good fuel and flow. Nothing plugged in the tank and no air in the system. It’s common to get air in the system after a filter change. Others have posted on here with gelled or algae fuel and thought that adding additive would fix everything. Remember it’s going to take some run time to get old, non treated fuel, out of the filters, fuel lines etc. We also had one person post thinking a cetane boost would also fix gelling.
Hope it’s an easy fix!