I have a 98 yr model Buick Riviera that will not start

Have you checked the battery? Do you have any dash lights when you turn the key?

If the car has not been run or serviced for some time then start with the suggestion above. (1) make sure the battery is good and has a charge. (2) check the battery cables at the battery, they could be loose or corroded. (3) If it still does not crank, you may need help......on newer cars, the security system might be keeping the engine from cranking. A late Riviera is worth putting a little $$ into to get it running, they are great cars. PS if it has the supercharger, check the lube in the front part of the supercharger before doing any driving...remove the plastic cover and there will be a nickle sized plug with a hex socket, unscrew and lube should be to the threads of the hole. GM has a special lube but there may be a substitute, do a Google search on how to lube the supercharger and you will find video