If he did the official update recently it should have updated you to 4.1U not 4.0U. If it was a disc update, that's a different story, but that would not have updated to 4.0 as no game has the 4.0 update yet. Make sure you know what FW you are on in the Wii settings.
But anyways, if you use the Trucha Bug Restorer properly, you should be able to get the trucha bug and ES_Identify patched into IOS36 so then you should be able to install preloader afterwards. After you use the trucha bug restorer I would suggest getting the most recent cIOS installed (rev14) and have the installer use IOS36 since you just put the trucha bug in it with the TBR.
After that if you still can't load games with a backup launcher like NeoGamma R6 or R7 (see edit), you could try running dop-IOS v7 and scrolling through the list of IOS's and seeing which ones are not updated to the most recent version or installed at all. Then try having it update whichever IOS's you can without the sig hash check. You can skip any stub IOS's and such and IOS's like 30 and 50 and 51. Also might want to check which IOS the HBC is running off of by pressing home in it and seeing what IOS it says there and skipping that one in dop-IOS as well. Not sure if updating that would stop the HBC from working or not. (though you could probably just reinstall it via bannerbomb/hackmii installer if it did) Also leave IOS36 alone since you already used the TBR on that one. (see edit) And for IOS60 you can install that with the sig hash check. (Do this before install preloader otherwise I believe you will have to reinstall it.)
Backup games shouldn't work through the disc channel to begin with at all since updating should have gotten rid of at least most of CIOSCORP and you most likely never had the IOS60 from CIOSCORP installed which is what 4.0 runs off of now. I'm not exactly sure why originals wouldn't work as well, but maybe it's because there are still some leftover CIOSCORP IOS's left and the original discs aren't working well with the mix of modified and unmodified IOS's or something. So hopefully running dop-IOS as I said will make all of your IOS's proper and at least fix the original game loading there.
edit: forgot you mentioned games still worked through usbloadergx so you should already have some cIOS above rev9 installed. Since that's the case you could probably skip the TBR step too if you want and just patch the sig hash check and ES_Identify in IOS36 with dop-IOS