OK! So after a bad accident in my Mercedes a couple weeks back I bought a new one, the criegslist ad said, use to start and drive perfect and won't start anymore (or very intermittently), I drove up, swapped the battery (wasn't the problem), tried turning the key on and off repeatedly and eventually after messing with the fuses and about 100 on/off cycles of the key, the glow plug light randomly came on and the car fired up in 20 degree weather. It ran great, drove it around the parking lot, parked, turned it on and off 5 times, glow plug light came on every time and started without issue. So I bought it. Came back to pick it up and again it wouldn't start, no glow plug light and I haven't gotten it to start since. The only upgrade the car has is something called a "Stage 2 chip" but otherwise is stock. I've scoured the internet looking for everything that could have to do with this problem and came up with alot of good options, but all have failed so far.

First I swapped the K-40, no change, then I swapped the Glow plug relay, no change, then I tested every wire and the ground to the glow plugs, all good, then I tested the glow plugs, they were all bad (odd because it fired up so well in 20 degree weather which should be impossible) but today thinking that had to be the problem, I swapped all the glow plugs and still absolutely nothing. I turn the key over, the k-40 clicks, everything seems function properly but it refuses to even crank.

The work around I found was that if you bridge the connection on the K-40 the car will attempt to crank as soon as you turn the key to the on position, but no matter weather I heat the engine or use ether ect, the car refuses to fire. At this point i'm completely lost, as a last ditch effort I will be swapping the Ignition and ECU from my parts car hoping that maybe the "Stage 2" messed up the computer or that the ignition is somehow faulty (which I see as highly unlikely) but any other opinions would be vastly appreciated!

You have to know that the key is good, the EIS is good, and it agrees with the engine module to give start authorization. I wouldn't waste time with anything else without crossing those hurdles first.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

Hmm, Now that you mention it, The key will no longer lock/unlock the doors/pop the trunk and the little red light on the key above the lock symbol lights up, how would you go about diagnosing a key fob problem? It initially accepts the key and allows to turn it to the on position, and I was told this model key could work even if it was dead. Could the Ecu have had some security setting since it was stone dead thats not accepting the key? or could this model actually need the key battery replaced? Might look into that. Either way, If I were to swap the ignition, ECU (and one other thing steering lock or something) from my parts mercedes, would that negate that problem since I know they all work?

Your battery is dead.