I bought a video card, I can't check it's name right now, but I think that's irrelevant as the problem happened with 2 other ones, one from Nvidia and the other from ATI (of course, I then changed them for free).
So, the problem here is that every time I connect the monitor cable (the blue one) to the video card, the monitor shows a message saying "Analog: Power Saving Mode", and the light turns from blue to orange. I'm currently using the computer with the monitor cable connected to the motherboard.
The video cards I bought were functioning nicely for the first few days, and around the end of the week it stopped working and showed me that message. I then changed the video card to the one I recently have and just kept it, because I though it would be something with the video card's heat.
I heard somewhere it might be because my computer can't support the video card. Yes, my computer is kind of old, the motherboard and processor and other things aren't really new or good, but I can use it like any other computer, except that without the video card I can't run any good games.

Current Computer's Specs:
Processor: Intel(R) Pentium(R) 4 CPU 3.00 GHz 2.99GHz
RAM: 2.00 GB
OS: Microsoft Windows 8 Professional Edition (build 9200), 32-bit
Video Card: Intel(R) 82945G Express Chipset Family (Microsoft Corporation - WDDM 1.0)

My first guess would be that your motherboard doesn't have the required PCI-express slots. The cards fit in PCI slots but I guess that's what's killing them, could also be something with them not getting enough power.

And for the love of god, just upgrade the entire thing.

Haha, money is the problem here. So the solution to make the video card work is by upgrading my motherboard?
And to do that, I guess I'd have to change the RAM type and the processor so it can support it?

Windows 8, 2GB of RAM

Okay Joseh, whatever floats your boat

Posting your mobo specs and the specific cards you tried might help.

This. Also, do the videocards have plugs for 4 or 6 pin power cords from the PSU? Because they usually need those to be plugged in to run.
How is your computer operating.

Wuh I was referencing Joseh's post...
Unless you are literally asking me, in which case Windows 7 64bit, 4gb of ram, i5 2500k, GTS 450 and 2TBs are not bad

Well, I don't know how to edit images, so yeah, 2.00 GB of RAM with Windows 8. Also, maybe it's because I use that thing where you can use hard disk space as RAM?
Also, one of the video cards I used was Ge Force 8600. I guess the others were equivalent ones from other people?
Also, remember that the video card worked for a few days, then it stopped working.
The video card I currently have is XFX One or something like that, and I don't remember the other ones I had.