Hi, PC started giving me often BSoDs and it failed to boot up. One Ram Module wasn't okay. I removed it & it went okay for few days. Suddenly it became very slow, laggish & unresponsive. But it booted up just fine. After using it for an Hour or so it would freeze.

I ran a diagnostic provided by Dell BIOS it showed an error; "2000-0123". Still booted up fine. Yesterday I ran a diagnostic test it showed different error; "2000-0146". It showed some text "Alert! Failed to initialize one or more disk during POST" but it booted up just fine after hitting F1. After 10-15 min later it crashed to black screen no error displayed. Even the Power button wasn't lit. 

I dont have any idea What is going on with my PC?

-Any help will greatly be appreciated.