How to repair the orange light

That’s almost always a failed power supply or a loose ATX 12V connector on most of these Dell towers -- See here as to why. At the time, Dell was hit hard. Check the connections to the power supply first and even look into disconnecting and reconnecting them. Also, check for bad capacitors. A lot of systems have problems with capacitors, especially older Dells. What has always worked for me on those to make sure it isn't a deeper issue quickly is to reseat both the 20/24-pin and ATX 12V connection to make sure it isn't an age-related disconnect. The cheap fix is a new power supply on these, especially when the fault remains after a connection reseat. Should it be a bad motherboard, it usually ends up being a recap most of the time, but depending on how long it has been rotting with the bad caps, it can sometimes ruin the board beyond repair.

If that doesn’t work, check the diagnostic lights on the back IO shield and take a picture of them to better understand what needs to be done. You can also compare the picture to the service manual to see if you can find out where to start.