Computer keeps rebooting, left mouse button rarely works

I just want to shout out what my recent experience is, since it doesn't make any sense to me at all.
If I can help at least one person having similar problems, then I'm happy.

So, my home build PC with Windows7 Ultimate 64-Bit suddenly started acting up after 2 years of solid use.
(The computer is pretty basic, nothing fancy except for an expensive graphics card, since I enjoy gaming)

Problem # 1: My left mouse button stopped working. No explanation how this happened, but restarting the PC did not help. I did not install anything new that could have possibly caused this.

Problem #2: After the second reboot, it would shut down by itself after showing the desktop.
The system restarted again by itself, but this time it didn't even boot up until the desktop. After this, the PC would reboot by itself at unpredictable moments: before BIOS, during BIOS, after BIOS, during W7 boot, after W7 boot, I could use the PC for a moment, but then it would reboot by itself over and over again.
Entering the BIOS and reviewing settings, it would again reboot by itself.

I started troubleshooting the hardware and to make a long story shorter, I disconnected the following parts one at a time to see how it would affect the unexpected reboots:
- HDD
- Graphics card (video from MB)
- WiFi PCI card
- DIMM memory

I knew I would see errors, but I was more interested figuring out if the PC would still reboot AND IT DID.
I went to the computer store and bought a new Power Supply. No improvement!
I went back to the store and bought a new MB and DIMM (the DIMM was showing some kind of bad contacts when I would tap it). No improvement!
It freaked me out and I wanted to start replacing the door knobs.
I didn't believe it was the CPU for some reason. While looking at the PC rebooting over and over again, I was wondering what the common factor was:
- the enclosure
- the CPU

Again, I didn't believe it was the CPU for some reason and could not believe there was a problem somewhere on the enclosure causing a short on the MB. So, what was left?
The tiny cables going to the front LEDs (HDD activity, power on LED, etc.) and the power on/off switch and reset switch. Several times I looked at the label of the tiny reset connector to the MB and wondered where the damn switch actually was.
I decided to pull the reset connector from the MB and BOOM, the PC fired up. No problems and it has been running stable now for several days without any problems!
It was the reset switch causing the problems all the time!
I started a new journey figuring out where the actual reset switch was located and it was really unnoticeable, right next to the big on/off switch. I never used it before and didn't even know it was there!
I pressed it several times and who knows, maybe I fixed the problem that it was undesirably, unexpectedly shortening its contacts, probably due to not using it!?

I put some research what a valid reason could be to use the reset button and I understand the philosophy behind it, but it caused me more headaches than solutions.
Disconnect the damn thing so it can't be used anymore.
Have you ever wondered why there are so many computer (enclosures) that don't even have that reset switch? Because in case you encounter a problem with H/W or S/W you want to shutdown the PC and not gently trigger a reset to the CPU. Shut it down and get rid of all your residual voltages to make a clean, fresh start: that's what you want when you restart a PC. Many computers will even interrupt the power to the HDD anyways with a reset and that doesn't help if you want to prevent any voltage spikes to the HDD.
With other words, a hard or soft shutdown does not make any huge difference for the life span of your HDD. Come on, for the period of time of use it? You don't want to use your HDD for 25 years to begin with, but I'm drifting off topic here.

It was an experience and hopefully you can get your benefit from it. If I would have known this upfront, it would have saved me two trips to the computer store and spending some money, however, I ended up with a new MB, stronger Power Supply and more memory

Oh, and by the way, the left mouse button? I totally don't see a link, but it started working again, all by itself!

Layback Bear, did you experience the same strange thing with the left mouse button? That part never made any sense to me.

Neither do I. I bet you it was something different, not related to the "main problem" and it was fixed by itself for whatever reason. Funny thing is, that's how it started.