losing $? check the income page, there are 2 areas which will take ur $ away: infra upkeep, fleet upkeep.
also, it depend on what race u are, i expect u r Terran, research Commerical n build Commerical infra is the easy way to grow.
of course, if u do the wrong thing such as research Commerical but never build Commerical infra... er.... then u wont get $ :)