remove the memory and check if you are getting the same error, if yes try with a different memory if you have two memory modules check with each. remove the cmos batter and power battery and keep th elaptop for 15 min , connect the direct power and switch on again
(1) check if you can see the wifi connections if not, (2) check if it is on airplane mode is on, if yes off it (3) check if the wifi is on or off (4) check if the wifi drivers are installed # check connecting to a wifi hotspot
Press and hold the reset button for 10 sec. it will restart and check after 5 min. if you are getting new wifi siganl. if not connect a network cable to the router ( LAN Port), and the other end to the laptop. check if the laptop is connected to LAN, if not the router is defective. if yes open the command (CMD or terminal) in your laptop and type ipconfig /all and press the enter key it will give the ip address and gate way enter the gateway ip address in the browser and check if you can access the router configuration page. login to the site and configure the wifi.
(1) Restart the computer. Immediately after the chime hold down the (Command-Option-R) keys until a globe appears. (2) The Utility Menu will appear in from 5-20 minutes. Be patient. (3) Select Disk Utility and click on the Continue button. (4) When Disk Utility loads select the drive (usually, the out-dented entry) from the side list. (5) Click on the Erase tab in Disk Utility's main window. A panel will drop down. (6) Set the partition scheme to GUID. (7) Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.) (8) Click on the Apply button, then click on the Done button when it activates. (9) Quit Disk Utility and return to the Utility Menu. (10) Select Reinstall OS X and click on the Continue button.