Low does not work, medium and high do

depending on car some have a fan relay or its your switch itself

I'm going to ask the first "obvious" question: are you sure the socket you're plugging into is delivering power? (Sorry to ask but it's an Occam's Razor kind of situation) Have you tried a different socket in the same room? Next, does the main power switch for the heater have different settings i.e. high, medium, low, high-high, high-low, low-low and have you tried those combinations? Next, pick up the heater (if it won't hurt your back) and give it a robust shake. Try the power again. Any luck? Keep us posted.

Have you checked the circuit breaker or fuse for the circuit that your heater is on? It's possible that you had something else come on that, combined with the current draw of your heater, popped the breaker. If that turns out to be the case, turn the heater switch from high to medium or from medium to low so that you're drawing less current.

Could be a bad switch or it may be high blower relay.

If the dryer has dual or triple heating elements, one element, or the relay controlling one element, could be open circuit, ( failed). mostly likely is a failed heater element. The elements work together or separately to combine the heat settings. there could be a high and low element, that do the different ranges. it could be that when it is on medium or high, it's really a lower combination of heat, and it may not be easy to observe, but on the low settings, the chosen element is completely open and failed and provides not heat at all. if medium and high are really low and medium, and low and medium-low is really nothing, then 1 element is probably open circuit. ( failed).

Heater core is partially plugged or the control valve for the heater is not working.

replace the heater fuse/breaker and, the whole resistor set (each resistor controls a different speed on the heater fan: low,medium, high speed

Could need a recharge.

It also could use a A/C tune up...there may be condensation in the system.

All cars are designed with a blower fan motor that pushes air through the ventilation system. This air is processed by a series of vents to direct the air to various positions. Example: heater, air conditioner and defrost modes. Most blower motors are power by a basic electrical circuit that utilizes a multi resistor or a solid-state resistor to control different fan speed modes (low, medium low, medium and high). If the resistor malfunctions it may lose one or more of the lower fan speed settings.
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There are two relays for the heater control fan,a low blower relay and a high blower relay.It sounds like the hi blower relay is bad.