Would a lower watt microwave help

Are there any issues with the direction from which the feeder cable (4/3 Romex in my case) enters the subpanel? I plan to have the feeder come up from below. Most pictures I see in the DIY books show the feeder coming from above. The panel I have seems to have plenty of room to route the hot, hot, neutral, and ground to their correct terminations. I'm just wondering why I never see examples of feeds from below. -- Jim

Yesterday, I replaced a ceiling light in my home (lots of knob & tube, the house is 112 years old), this light seems wired on a newer circuit. The power comes into the ceiling box, and attaches to another wire that runs down the wall to my switch. The new light fixture ran all day, and then was shut off for a few hours. I went to turn it on and the light bulb flashed like it had just burnt out. I replaced the bulb and still nothing. Today I replaced the wall switch, and still nothing. I even tried attaching another fixture to the circuit, and stll nothing. Any suggestions, other than calling an electrician? I consider myself to be an above average handy-man, but hardly an expert. Am I over looking something? Thanks everyone!