PC will not boot (no power) but I do see some lights on.

So I opened it up to clean out the dust, like I have a million times and after putting it back it's completely dead other than the cat5 connection light and a green light on the bottom left side of the mobo.

No idea what I did but everything seems to be connected fine.....

Anyway, I'm guessing it's probably the PSU...or mobo but I don't know crap about hardware.

Any ideas?

just a can of air.

So if i understand correctly when you press Power button nothing happens, right?

Did you remove any components before dusting or did you just blow the air inside the case?

Check the power, power led, reset and hdd led cables again. If theyre definately plugged in correctly than unplug the power one and touch the two pins with something metallic(screwdriver, knife) just be careful not to touch anything else.

If it doesnt help than go through the whole checklist jsc linked above.