Sorry you’re having this trouble. I have a couple of possibly not useful pieces of information to see if I can help you. It sounds like you have a connection problem.
First, are you using the same download cable as you used the previous day? Some cables are charge only (not data) and I tend to rid my house of those!
Second, (kick me if you want, but…) is your Mayfly switched on? The Mayfly has a manual toggle on/off switch and this could cause your error.
Third, there’s a switch on the top edge of the board that exchanges between an external power source vs “lipo”, keep that on the lipo option. I have heard of some issue with frying boards that are set to external power when connected to USB (or the wires were backward for that colleague, but you have to be on lipo or it will bypass the programmer).
Fourth, have you selected the Mayfly under the “Tools” menu? If it isn’t in the tools menu, you may need to re-install the drivers.
Fifth, every time you connect any Arduino board to a new USB port on a Windows machine, it treats it like a new piece of hardware and assigns a new com port number. It looks like you were connected to COM3, but if you are in a different USB hole on your computer, it may now be a different port number. Since you re-installed everything, I’m not sure what the expected behavior is (I’m a Mac user…but I’ve seen this issue with my students).
Let me know if any of those ideas help.