how much does ORI set cost for w980i?

i'm a w980i user; its 1 yr old...recently i found tht my phone switch by it self automatically....then i had to switch on back....it happens several times...i call the shop where i bought the phone from..he said might be firmware issue...or could be battery....i need help on this since the warranty it over...should i try to download latest software update from SE site or give to phone shop...if can i wanna do by myself instead of paying...my latest firmware is: 1205-1464 R3DA028080908.

i did try to search latest firmware by using via phone it stated i have the latest software.

need advises.....