go to your starter and check your fusible links to see if one of those is broken those 2 or 3 wires go to your inside switch and fuse box.
Your question isn't very specific- if you have wiring problems, you could start at the fusebox and see if anything is burned- that is an old car and it could be anything- I love Fieros, but they are overly complicated- over-engineered a la GM-
You say no power into the car itself....do you mean dash lights, wiper blades, radio, etc.? If this is the case then check the fuses first but it is more than likely your Alternator belts or your Alternator. If the Alternator belts are the wrong size or worn out you could lose all electrical power to the car and if it has been going out it will drain you battery. I am going through this same problem right now with my 85 SE. Hope this helps.
Looking for a Used Fiero in your area?
CarGurus has 72 nationwide Fiero listings and the tools to find you a great deal.
Search Pontiac Fiero Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Pontiac Fiero Experts