From that explanation - if solenoid is energised then you cannot change from high to low or low to high. This is the condition the OP has currently as solenoid seems to be energised as it has 12v applied. Not sure how you would check if the shift fork has been rotated or not

 

Sorry that I havent been back here for a while, I've found out it was the Transfercase module causing these issues this whole time...

 

Hey guys, sorry i haven't updated my post after finding out what's wrong with my high/low range flashing. What I've found it was the Transfer case module, I took my meter at the yellow connector and tested the voltage that sends the signal to the transfer case solenoid, it was flashing 12v to 0v which indicated that the module is sending the incorrect voltage to the solenoid. I ordered the transfer module from ebay which came off from the Range Rover. I wasn't sure it was going to fix it but it did, all the light went away. I heard the solenoid engaged and switched to high range.

In my previous comments posts i did find corrosions on the yellow connector and inside the Transfer case module but a little bit on it, I did not think just a drop of water can cause the module to go haywire. So if you guys run into this problem make sure you check the module and inspect any signs of corrosion, and if you do, replace the module!! I hope this save some headaches for you all.