My main fuses overheat if I use my ac and oven at the same time or the ac and dryer. The ac, stove and dryer run off two 60 amp fuses. They remain cool but the main 100 amp fuses { the pull fuse holder} is extremely hot to the touch. What could be the cause?

We just purchased a modular that has been empty for atleast 8-9 years. Had the electricity turned on and 2 bedrooms a bathroom, hallway between these rooms and 1 wall plug in the front room have no power. Have checked the breakers power coming in and going out there is power there. Have pulled every plug and switch in these rooms and checked for wiring. Also pulled the light fixtures and checked those. These are all on the same side of the house right in a row. Have flipped the breaker off and checked every plug and switch in the house to see if something else is on this current, but there is not. We are at our wits end on trying to find what the problem is. Any other idea's to try?