after years of not touching a computer, the act of heating and cooling can cause bad connections. You basically just had to reseat the RAM.
If the MB posts and there is a hardware fault, there will almost always be a beep code. No beeps (after reseating all of your cards)points to power supply or MB CAPs almost all of the time.
to the OP: As far as replacing CAPs... it's worth the time and money, if they're available locally. I replaced the caps in a router a few weeks back because I found a shop that had suitable replacements at like $0.50ea. I finally shitcanned my old printer for a new one, but spending $2 on CAPs for it gave it another 4 years of use. I went so long without printing photos that the ink dried up and ruined the print head on one of the colors... that's the only reason I replaced it.
I will be the last person to die in my lifetime.