|The short answer....|
With the AC cord uplugged from the computer, or with the AC otherwise switched off to the computer, you could try making sure all ram and cards are all the way down in slots, and that all connections inside the case are okay, and if that doesn't help.....
Your power supply is probably in the process of dying. If you replace it your system will probably work fine.
I checked and your power supply is a standard sized standard wired ATX power supply.
Example replacement PS:
You can replace it with any decent standard sized standard ATX PS with the same capacity or greater.
Standard (PS/2) power supply size - 86mm high, 150mm wide, 140mm deep, or 3 3/8" h x 5 7/8" w x 5 1/2" d , or very close to that, though the depth can be more or less for some PSs.
Don't buy an el-cheapo PS.
See response 3 in this:
Since you have added a video card, or you changed your previous video card, you MAY need to get a power supply with more capacity.
Your power supply must have at least the minumum capacity required to support a system with the graphics card you are using installed, or the max graphics card you might install in the future.
(Onboard video - video built into the mboard - IS NOT A CARD ! )
If that info is not in the ad for the video card, you can go to the video card maker's web site and look up the specs for the model - often under system requirements - the minimum PS wattage, and, more important, the minimum amperage the PS must supply at 12v is stated. If you don't find that, any card with the same video chipset including any letters after the model number has very similar minimum PS requirements. Some power supplies have two or more +12v ratings - in that case, add those ratings to determine the total +12v current capacity.
If you're a gamer...
In most if not all cases, the max capacity rating of the PS is an intermittent rating. It's recommended that you do not load your PS to any more that 80% of that rating if you are going to be using something that puts a constant load on it, such as playing a recent game for hours on end. In that case, you multiply the min capacity stated for the system with the particular video chipset on the card by 1.25 to find the min. capacity of the PS you should get.
Why would it fail ?
- power supplies tend to fail as they get older in any case - the electrolytic capacitors in them deteriorate over time, and in some cases were improperly made in the first place .
- the video card you added may overloaded it.
Apparently this model comes with a 305 watt power supply.
"...upgraded PCI 256mb vid card..."
Depending on which video chipset it has, the power supply may not have had enough capacity to support having that card being installed, and if that's the case, the power supply is trying to run at 100% of it's capacity all the time the computer is running. Computer power supplies are not meant to run at 100% or their rated max output continuously - that max is an intermittent rating - and eventually the power supply is damaged and fails.
Manuals - Service Manual
"The power on button on the front of my computer is blinking orange every second or so..."
" Blinking amber
A power supply or system board failure has occurred.
Check the diagnostic lights to see if the specific problem is identified. "
You may also have diagnostic leds that have lit up in a pattern that yield you more info - take a look at the info there.
Also in that Service manual..
- you have a 305 watt power supply, originally, of course
- there is a single double row USB header on the mboard, for two USB ports. You have either just two front USB ports connected to that,
or, you have an optional Media Card Reader in a 3.5" bay.
If you have only the two front USB ports, no card reader, probably, each port is connected to it's own USB port connection on the USB header. In that case each front USB port can probably supply the full USB spec max 500ma of current.
If you have the optional Media Card Reader in a 3.5" bay, one USB port connection on the USB header is for the card reader, and if there are two USB ports on the card reader, those two USB ports share one USB port connection on the USB header - they are in effect two ports in a USB hub, not directly connected USB ports - those ports cannot supply 500ma for each port - some devices that require more current will cause the bios to generate an overcurrent message when you plug them in - not all USB devices will work in a hub that connects to only one USB port connection in any case.
You are likely to get the overcurrent message from the bios when you plug some USB devices into those USB ports.
and - sometimes the wiring between the USB header and the USB port is inadequate, whether you have directly connected USB ports or not, and not all USB devices will work properly with those ports. You MAY get the overcurrent message from the bios when you plug some USB devices into those USB ports.
The USB ports on the back of the case that are built into the mboard should work fine with any USB device and you should NOT get overcurrent messages when you plug something into those.