Hi,
Not sure what the problem is, but if you have a way to try a larger adapter, it's an idea although it may just be covering up some other issue with the system if it works okay with the larger wattage AC adapter.
Hoping you can try it out first before buying one in case it doesn't work out, but the U.S. eShop site is still selling the 180w adapter used by the G75VW and some other models which will still has the correct plug size for your G74Sx if you want to try it.
AC Adapter link is below for your reference and you can probably find it from other websites, but again, not sure if that will solve the problem you are seeing and don't know why your adapters are not working now.
You may also want to check and provide the ratings under your AC adapters like 19V, 6.32A, etc. just to make sure everything sounds normal there since it is possible the new adapter you just purchased was not the correct wattage.
Feel free to check around more and get more suggestions, of course.
Good luck!
http://store.asus.com/us/item/201412AM300000085/A47375-ASUS-180W-G-Series-Notebook-Power-Adapter