Aspire 4738ZG turns off on windows but runs fine on cmos setup

my computer aspire 4738ZG laptop turns off immediately after turning it on but when i pressed f2 and running cmos setup it doesn't turns off (it runs continuously), it will only turns off if i pressed the power button again. already checked the fan for clogged, check the ram (already installed a good working ram) disconnect the hdd, reseat the processor and apply new thermal paste - but still it turns off immediately after turning on. i want to update the bios but when i boot on other devise it turns off immediately.

thanks in advance....