Similar problem with Optiplex GX270

On power up, I hear 2 quick beeps, the fan starts, then quiets down. Steady yellow light on the power button, no LEDs lit on the back, (possible pre-BIOS failure??!!). Had the computer open all afternoon before this happened. Wanted to install a new heatsink fan assembly, but Dell sent me one missing the 'thermal grease'. So I cleaned the old fan and reinstalled it with some difficulty. I also tried to install a new video card, but Dell sent me one that doesn't fit in my computer. With Dell tech support on the phone, I tried to fit the new card in somewhere for quite a while before he concluded it wouldn't work. Pulled out/reinserted a couple slot fillers, pulled out/reinserted the card cage several times. I've rechecked everything inside a couple times, but still get the yellow light, black monitor, keyboard and mouse don't work. HELP! (btw, my kitchen faucet is dripping furiously, even with the water supply shut off. Any suggestions for that would also be appreciated.)