The a/c or heater on my 1998 chevy blazer will not turn on at all.?

Best choices, check fuses first, tap lightly on blower motor with wooden end of hammer, if runs blower motor bad. if neither of these help take in to shop to get OBD2 check for parameter readings on sensors.etc. could be dash module unit or even ECM bad. Don't guess, replacing parts will just cost more. Just not like the old days anymore.