W10 for mobile, unable to update. Please help.

[vineet_vpns12]

Have w8.1 denim update.
Downloaded window insider.
Signed in with MS id.
Option pops up, slow n fast ring.
I tried with both, bit it just says, your phone will reboot in 5,4,3,2,1... And then it gets crash.
I did a hardset and also tried reinstall of Windows insider . Nothing worked for me.
Kindly guide me.
Ty

 

[jfa1]

What phone are you trying to install the os on.?

 

[vineet_vpns12]

what phone are you trying to install the os on.?

lumia 520 unlock (india).