I had an old 7 year old dell that died 6 months ago. The light in the front would turn yellow, but I wouldn't hear the processor like you do, the system wouldn't turn on. I later found that one of the capacitors on the motherboard looked to have been spoiled or just broke from the bottom. I tested the power supply and it was in working condition.
Sometimes, what works is to re-seat the RAM, processor, and all the cables and try again, that's a trick used for old dell computers.
By the way, my dell gave me these yellow light problems before, but it would turn on after 20 minutes. My yellow light problems happened after a power outage from a lightning strike, while the pc was on. One day I turned it off to test some case fans and it never again turned on. I guess the broken capacitors on the motherboard just finally gave out. Replacing the motherboard, etc. on the computer wasn't worth it.
Good luck with yours, but my old dell died.