Hi, two years ago my Arduino uno stopped to work and now I found it. The problem is this - my laptop can’t see my Arduino. I was trying to write the bootloader but without success. I don’t want to throw it away and by new one because I think this board can be alive.
Also when I turn on my board, the L and On leds are working but not blinking.
Let's try to narrow down the problem, use another Arduino like the one you have and see if your laptop sees it, if so it is your board. In that case you can use the working board to program the failed unit.
Can you remember what kind of project you were working on 2 years ago?
Regarding the L led, it depends if the currently loaded sketch actively controls it; if it's configured as input, it's quite normal that it is permanently on. I have the same behaviour on my original Unos but my RedBoard behaved differently due to different electronics diving the led. So it's not necessarily an indication that something is wrong.
Note that you more than likely have abused the board in some way (not intentionally) and other components might have been damaged as well. You should definitely mark the board as "unreliable" because it might suddenly give problems for no obvious reason.