ubuntu freezes during shutdown

My dual-booted Samsung 140 netbook pc(https://wiki.ubuntu.com/HardwareSupp...hines/Netbooks) is working well with 14.04.4 lts. but sometimes when I shutdown(or during Reboot) my pc, the screen flickers with unrecognised characters(see photo1) and it never shutsdown(or Reboot).In this case I am to press the power button to shutdown..If hold down "ctrl+alt+del" it shows((see photo2) this..

starting store software rfkill state [ok]
starting emergency keypress handling [ok]
starting store sound card state [ok]
stoping store sound card statestate [ok]
stoping store software rfkill state [ok]
starting emergency keypress handling [ok]
stoping emergency keypress handling [ok]
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I am facing this problem from past few weeks. It happened at least 15 - 20 times a total.

did anyone face the same issue? anybody has any idea how to fix this??

Regards.