My nissan hood was open for about 15-20 years and i want to know is it safe to start

Normally, the cable snaps off from behind the cabin release lever. In that case you can pull the cable end with Locking Grips. If it has broken at the hood end, and they have a history of it, there are videos in the link to get in through the grill.

https://www.google.com/search?q=2012+Nissan+Murano+hood+won%27t+open+after+pulling+hood+release

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Factory or aftermarket remote start system? Does it still lock/unlock the car just not start or is it not working at all?

Try disconnecting the battery for a couple of mins to reset all ecm's, then hook back up and try it...

There is no need for power to open the hood. Your cable may be streached, or in need of adjustment. Have someone push down and up on hood itself while pulling the hood release lever.

you have a rev limiter on that car. DO NOT OVER REV. the engine. The clacking sound is more then likely your valve tap-its from being over heated. Replace your thermostat and make sure you change your coolant every 2 years. Sounds like your thermostat is stuck open. Replace your thermostat every year or 2.

If the cable is broken or stuck, you will have to try to access the latch from under the car - or take the front bumper cover and grille out.

Duplicate question.

I know a trick from a local body shop. If you have a sawzall with a metal blade, then cut the latch to open the hood, and go to a salvage or junk yard to get a replacement and install. Be sure to put a new cable in to replace the broken one, of course.

It is 20, and 10 years past its designed life, this stuff happens. You need to figure out whether the latch cable has broken or the latch itself is bad. If the cable is bad, you should be able to reach up under the dash, find the cable coming from the back of the lever and pull it out from the inside. If it comes freely, then you know it is broken but do NOT pull it all the way out. If however the cable is good but the latch is broken you are going to have to get at the latch via under the bumper or through the grille, and unbolt it or the male prong on the hood. Some extensions and swivels will come in handy for your socket set. When you get the latch or prong loose the hood will open

There is also a remote possibility that the spring which pops the hood up when you pull the lever has broken and the hood is actually unlatched so long as the lever is pulled. Check this by having someone pull and hold the lever from inside while you try to open the hood and release the secondary.

the hood should stell open no matter what un less the cable is broke i have the same car all that happens when the alarm is set off is the horn blows and the lights flash it doint stop the hood from oping