Desktop Boot and Lockup

My brother dump this Pavilion 24 all-in-one on me, the system would boot to login screen, after entering pin the system would go to Black Screen showing only the mouse point and malware window for Driver Updates,  (Note he missed McAfee expiration date)   so I was able to get into safe mode but not with networking and uninstall this AutoRetrive Driver Update App using the control panel,  So now I need to get safeboot with networking to download Malwarebytes,   went to msconfig and changed to selective startup with networking but that wouldn't happen,  so in one of my attempts to modify startup sequence I believe I selected Diagnostic and now the system can't find the Pin Id,  so using the system process to get to Command Prompt which requires several power up and holding the power button the system started making this hidious beeping which sounded like 3 groups of 3 long,   After that the system refuse to boot,  per system procedure I've disconnected the power source,  I've press the power button for 15 sec. then reconnected power adapter and get the green led above the power adapter connection,  I then hit the power button which lights up,  get no system post, nothing comes up on display but I can hear hard drive winning up and I noticed that the LED for the power adapter starts to Blink,   1 long-2 short-1 long and goes out but the main power button light is still on,  Anybody got any ideas on what wrong with this system