My furnace cycles once, then won't ignite again. What could be wrong?
A red light flashing 7 times typically means the furnace is in lockout mode, which based on your description seems to be your situation. 

There are many things that could cause the furnace to fail to light, each of which requires its own diagnostics to determine if it is the problem.  

Since it sounds like you don't know much about furnaces, your best bet would be to contact a local licensed HVAC company. 

Things that could cause a furnace to fail to ignite include, but are not limited to...


Gas off.
Electricity off.
Clogged burner orifice. 
Bad flame sensor.
Bad pilot assembly.
Bad igniter.
Bad control board. 
Bad gas valve.
Restricted combustion air supply.