I've started to put my HTPC to sleep and the power led blinks on and off which I do not like. I would like to have the led gradually get brighter and then darker instead of blinking on then off. I believe a pc power led uses 5V and this led is on and off for about 2 seconds.

From what I know a properly sized capacitor added in series with the led would cause it to gradually fade until it reaches the minimum voltage and turns off. I'm not familiar with anything that would take 5V and provide a low voltage that increases over time to have the led brighten gradually. Is there something simple that can do this? I'd rather not have a solution that requires external power or logic.

 

A capacitor in parallel with the LED will make the on/off transitions slower. I don't think you'll be completely satisfied with the result but, given your constraints, it's about the only thing to try. Make sure you get the polarity of the cap correctly oriented with the LED's polarity.