|If the ram modules or the circuits of ram slots are damaged they'll never work again. |
The modules could be fixed in theory but it's cheaper and a lot less trouble to just get new ram or use undamaged used ram.
If you're fortunate, installing undamaged ram in undamaged ram slots will get your computer working again.
You may or may not be able to see evidence of damage on the ram modules and in the ram slots - damaged or missing (vaporized) contacts, black carbon deposits. You may need to use good lighting and something to magnify what you see to see that.
Installing a ram module backwards in a ram slot and then attempting to boot the computer will definitely produce damage on both the module and in the ram slot that you can see.
If the circuits of both ram slots are damaged the mboard must be replaced.