Hasards dont come on on a 2000 isuzu trooper

No need to panic-this can SEEM TO be caused by a couple of things, but it is fairly simple to determine exactly what is causing this flasher circuit condition.
First, turn on your flashers, however you have to do it, and walk around the truck to check that all bulbs are working (at least one on each corner). Turn signal and hazard flasher relays are thermal circuit interrupters and are current sensitive and will not work properly with too few or too many bulbs in the circuit. (This is usually a big problem when switching over to LED lamps, as LEDs only draw a fraction of the current that the bulbs do. This causes the relay to either not flash at all or flash very fast and triggers warning circuits on newer cars) If there is one or more bulbs out, they must be replaced.
That being said, I doubt that alone is your problem. Here is a general automotive wiring primer aimed at the turn signal, hazard, stop, and running lights on most all motor vehicles.
Hazard flashers are required by D.O.T. safety standards on all motor vehicles that may ever be used anywhere near a public road. They are also required to be able to be used without the ignition key. This means the flasher circuit for hazards is fed thru a fuse that connects straight to the battery and is energized at all times.
Turn signal circuits often share the same flasher relay as the Hazards, even though the power for them is switched through the ignition key. Power for directional blinkers connects to a fuse, then the ignition switch, then to the battery.
So, if you have to turn on the turn signals (is the key on?) to get hazards to work, that means they are not getting power direct from the battery, but can get it when the turn signals are on because they both use the same relay. This is usually the case on all vehicles; If 4-way flashers and turn signal are both on at once, the 4-ways override the turn signal and force all signal bulbs to flash. The turn signal never forces one side of the hazards to stop blinking.
So, where does that leave us? You simply have a blown fuse, my friend. The hazard lamps fuse may also power the cigarette lighter, dome light, or other "always on" accessories. This varies with make & model, but the Hazard Lps fuse is usually well marked in the fusebox. If the fuse blows again shortly after being installed, do not put in a larger one! Try one more. If it also blows immediately, there is a problem with the wiring, or a bulb could be in wrong and shorting to the socket ground. Try removing all the flasher bulbs and trying the switch(it won't flash or "tick-tock") again. If the fuse does not blow, you have found the problem. Good hunting!