Sounds like you mean your WiFi keeps disconnecting, not your Internet. The latter would be an issue with your modem or with your router needing to be reset. If your connection comes back on its own that's obviously not the problem.
Look - WiFi is pretty great for web browsing on mobile devices and laptops but if you want to connect a desktop to the Internet it's about as bad of a choice as you can get. If it's at all possible to use Ethernet you should be, but I suspect you know this. The only way to improve your situation is to start moving the two devices physically. You said if the adapter is in the front of the PC it does better... what kind of adapter is that? Is it a USB one? Those have tiny antennas in them, you'd be better with a PCI(e) adapter that has an external antenna you can move around as needed. If it's possible to move the router you may simply be getting interference from a wall. Do you have neighbors with WiFi? Maybe switching to a different channel could help, but if you have a lot of neighbors then all the channels are used so it's unlikely to matter. Of course if you had 5.0GHz (802.11ac or 5.0GHz 802.11n) WiFi then you won't have as many competing networks, but the range is lower so 2.4GHz may be better.
If none of those end up helping and Ethernet is not physically possible I would suggest you look into powerline adapters. All you'd need is an extra outlet near your PC and the router and two Ethernet cables then you'll end up with a completely wired connection. Throughput on these devices has improved greatly and you can easily get over 100Mbps.