When first switched on (plugged in etc.) turning front dial from 0 to 1 the machine should pulse for about a second (Ie motor starts then stops). If you do not hear this then it is an electrical issue. Checking plug fuse is the correct first step. If that is ok the it is internal which means some skill and knowledge and opening the case (quite easy but about 16 screws). Problems could be 1) broken switch rod, 2) broken on/off switch, 3) damaged cable 4) damaged motor. Other than the switch rod you really need a multimeter or similar to test parts. If you have skills then all parts are available and cheaper than scrapping the unit. If you do not have the skills then Google Repair Cafe. This is an international organisation of volunteers who will help, advise and repair, often for free. (Other than the cost of parts) There may well be one near you (there are thousands around the world and hundreds just in the uk.
Remember, old Karcher never die, they just need repair. Sometimes not economic if you have to pay a shop to do the work but Repair Cafe is the way to go.