My desktop cannot boot. Nothing displayed, I cannot enter its BIOS. I can only hear a beep out of it
"3 singles and then a double" 1-1-1-2 doesn't fit any beep code pattern that I could find. Are you sure you're explaining it correctly? Are they long or short beeps?
Its 3 long beeps and then 2 short ones. I know cuz I too have looked up the internet and could never find the code anywhere.
Beep codes vary from manufacturer to manufacturer. I've worked on computer before where three long beeps stood for a failed RAM module. In looking at the Dell beep codes, I found that 2 short beeps mean missing RAM module. Keeping in mind that the issue could be several other things (failed mobo, bad power supply, bad graphics card, etc...) Try this:
If you have some known working and similar RAM lying around, try taking all of the RAM out and replacing it with the known working RAM. Then turn the computer on. If you can see something on the screen and you don't get any beep codes (other than the single beep) you know that at least one of your RAM modules is bad.
Law of Logical Argument: Anything is possible if you don't know what you're talking about.