After installing a graphics card, DDO runs badly and crashes

[Fallingleafe]

O'zzio
Operating System: Windows 7 Home Premium 64-bit
Processor: Intel(R) Core(TM) i5 CPU 650 3.20 GHz 3.20 GHz
Memory: 4GB
Graphics Card: NVIDIA GEFORCE GT 630 directx compatible

This is my system spec. Before that, I was using the Intel(5) integrated HD graphics card, running DDO smoothly on high settings. I then installed the above graphics card and managed to run one raid of the Shroud with Direct X 11 enabled and features all on Very High. It went as smooth as could be.
However, the very next day, after changing nothing, absolutely nothing, DDO began to show black screens, stutters and sudden crashes which would cause BSOD's or require a forced shutdown.
Today, I attempted to play DDO again and on the settings I used to play at using the integrated graphics card - being on high and very smooth - I can barely play. In fact, I can play only moderately well with everything on Low, which clearly should not be happening.

I have installed all the newest graphic card drivers. Repaired DDO graphics before log in. Checked my entire PC for updates. Checked wires and connections. Checked to see if I installed the graphics card properly. I have enough power from my power supply. It is not overheating.
I even took my PC to the store where I bought it to get it checked out and they said everything on my PC was fine, it may be the monitor that is the problem.
This may be the case because other online games, even f2p basic FPS are causing the same lag, black screens and forced shutdowns. However, I am often getting a message stating that I have a problem with my graphic drivers, even thought they are fully updated and the PC tech guys at the shop today stating that everything was apparently fine with my PC.

So I am wondering if anyone knows what may be wrong. It is extremely annoying because before I installed this card, everything was working fine and I could play games and watch DVDs etc on my PC with no problems, but now I always end up with a crash and a restart, even with just playing low graphic simple games.

I am going to the store again tomorrow and taking my monitor for a check, but with the message appearing about my drivers, I am completely unsure as to the real problem.

[Dulcimerist]

Could you please post your full DXDiag report? That would provide a lot of helpful information so we can help you better.

Your system originally had Intel graphics integrated into the motherboard, and then you purchased and installed the nVidia graphics card in an expansion slot.

What wattage and brand of PSU do you have? (Some OEM systems, Dell being one of the more notorious, use the bare minimum wattage PSU. This makes PSU blowouts/brownouts common when users upgrade components in those systems.)

Did you go into your BIOS to disable the onboard Intel graphics, and then completely uninstall the Intel graphics drivers?

The monitor shouldn't be the problem.

[Missing_Minds]

What wattage and brand of PSU do you have?

This is what I'd really like to know, as that is my first suspect.

[Fallingleafe]

Aye that was it, the PSU.
Long story short, I had to replace my entire PC and am now on a brand new one which seems to be running DDO very smoothly, though I have having trouble getting DirectX 11 to work.

EDIT: Problem fixed.