Disconnect the ESP8266, see if it detects.If not, assume bad hardware and buy another - $1.50 serial adapters have a non-zero DOA rate.
Yes, test it with just the CH340G and see if it detects. If it does, then you know the USB serial adapter is fine, and that implies that the problem when the ESP8266 is connected is due to the load from the esp8266. If it doesn't, you declare the serial adapter dead and buy a new one. I buy those things 5-at-a-time. Uh - you are using a 3.3v serial adapter, right, not a 5v one? The esp8266 is a 3.3v device and is not 5v tolerant. Most 3.3v serial adapters are not able to supply enough current to power an esp8266, so you will probably need an external voltage regulator to get 3.3v for the ESP8266. Which version of serial adapter is it? (link to listing or post pic) I like the ones that look like this one (no specific endorsement of this listing) https://www.ebay.com/itm/USB2-0-6Pin-CH340G-Converter-for-STC-Arduino-PRO-Instead-of-CP2102-PL2303-To-TTL/191146797242 - with the little switch for voltage. But that still won't power an ESP2866 at 3.3v, it's just the nicest of the el-cheapo serial adapters.