Can someone please help me, my dell inspiron 14 3000 series 3458 with core i5 5200u and vga nvidia geforce 820m will shut down after a few seconds i turned it on, is it really a motherboard issue?because i already try to remove ram and give a new thermal paste on processor
Are you seeing any flashing lights or hearing any beeps? It does not sound like a heat issue where reapplying thermal paste will help, at least not if it happens right away before the system has time to warm up. Possibly RAM, so remove and reseat the RAM. Also run diagnostics on the system if you are able to get it to boot. Restart the system and at the Dell splash screen start tapping F12. Run full system diagnostics. You can also try resetting the system. Disconnect the battery and unplug the adapter. Press and hold the power button for 30 seconds, then reconnect everything and try again. Also remove the CMOS battery (coin cell) and leave it out for at least 15 minutes (Intel recommends 30). Better yet replace the battery after leaving it out for the same amount of time.
Did this start after you made any updates to the system or possibly after reapplying thermal paste (I believe you said you already did that).