n70 dead

n70 dead
when come on my shop it is in white secreen in some time and some time lcd work proper then i put some paste on lcd ic and give heat to it
i put the air rotter of my smd station on 3 and hear rotter on 4
and give hear to it about 30sec only.
then i put lcd on it and and when i switch on the mobile only for one sec, mobile on and show white screen and then automatic turn off,
now when i push the swicht phone does not respond
and when i put charger in it also phone does not respond
then i check on ufsx
then it is also shows ist boot err
please help me
i also check voltage on on-off switch
there is no voltage on it