New case/power supply...having some issues

My computer was bought a couple years ago, HP m7470n. The only changes I've made so far: New graphics card (GeForce 8600 GTS), an Arctic Cooling fan, and most recently a new case and power supply. It originally came with a 300W, I only upgraded to 400W for now.

The case swap wasn't too hard, but after hooking everything back together I've ran into some problems. My monitor claims it's not getting any feed from my graphics card, and both my C and D drives aren't seeming to be getting any power, along with my mouse and keyboard.

Is this a defective power supply or is it more complicated? I will be asking around other places and people, but I want to get as much advice as possible (as I'm still pretty new to setting up my own rigs)

I changed my power supply last month from a 300 to a 400 and it went pretty smoothly except one ribbon connector I got the wrong way around which stopped it working.
They have a red stripe along one end which should in most cases be closest to the power socket.

Are you sure the connections are the same as before and checked in the bios that everything is detecting ok ?

You could check your local library for a book on pc assembly mine is "Build your own PC" by Morris Rosenthall
They usually cover the basics and are well illustrated.

May be defective - but be sure to check simple things like are the connections tight? do you have it on the right power setting for you area - most come with a US and a European toggle - and is the power switch on the back of the power supply on ( happened to me once when I bumped the switch while moving the tower - took me an hour to figure it out)?

It could be many things.

Make sure there are no metal stand-offs under the motherboard, that don't line up with mounting holes (therefore shorting out the motherboard)

Some Dell computers use a non-standard power connector on the motherboard. Maybe the HP is the same. I have seen listings for power supplies designed for HP - this could mean they (and therefore, their motherboards) have oddball connectors.

As mentioned above, make sure every cable is inserted properly. It's sometimes possible to put a ribbon cable in upside down. This can short one of the voltage rails.

Thanks for the advice. As far as I know everything is plugged in where they should be, and the motherboard has no possible way of shorting out...we've made sure a few times.

It just boggles my mind that my graphics card itself is getting power (lighting up, fan moving, etc), but my monitor is still saying no Input signal.

I guess I will have to hit the books on this one, since company support hasn't helped much at all...or I'll have to do some more trial/error finagling.

Thanks again...if I have any more questions/problems I'd be sure to hit this forum up.

***EDIT***I got everything working, and honestly I can't tell you what I did to fix it haha...it's like it felt sorry for me and got itself working. Thanks for the help

Basically, on most monitors/video cards, there is a wire in the monitor cable that simply needs to be connected to "ground" (common) to detect that the monitor is connected to a video card. Most of the time, this has nothing to do with whether or not a video signal is actually present. (on some monitors, you can even plug the cable into a video card that's sitting "on the bench" (not installed) and the "No Input" message will go away.)

So, that indicates that there may have been a bad ground somewhere in the circuit. This can be a whole bunch of things. For example, sometimes, to make things easier, a motherboard will "cheat" and use the ground connection through the mounting posts instead of a trace on the board. So, in the process of checking the mobo, you may have done something that re-established the ground through some connector.

I should have mentioned before, that not only should you make sure that no "extra" posts are under the mobo, but that you should also make sure to use all the stand-offs and screw them all down. (although that isn't always necessary)