C7800V2 Connection Drops multiple times a day

Thanks everybody. It seems like the 30-30-30 hard reset procedure may have solved my issue so far. Now, I can login to my admin panel wirelessly (remember, I wasn't able to even login when connected with a cable directly to the modem) and most importantly its stable, doesn't drop anymore, pretty fast and I can configure my router. All of that was not possible before. I may still ask my ISP to check on the firmware and my personal decision is, to replace it with a modem and separate router on the long run.

I followed all instructions/ solutions on a page (doesn't let me to leave the link here but its ok, just google "Routerlogin.net not working and follow appulas) until Solution 8, Part 2 hase solved my issue, here are the details that I followed exactly like this:

If you cannot access Routerlogin.net even after the factory reset, then you need to perform 30-30-30 reset (which will clear out the NVRAM of the router and thus solve the problem).

1.Make sure your router is powered on and no cable is connected to it except the power cable. Disconnect every device PC, laptop, etc. from the router.
2.Now press and hold (through a paper clip or a similar object) the Reset button for 30 seconds.
3.Now, while keeping hold of the reset button, unplug the power cable of the router and keep hold of the reset button for another 30 seconds.
4.Then, while keeping hold of the reset button, plug back the power cable and keep hold of the reset button for another 30 seconds.
5.Then release the reset button and wait for one minute.
6.Now unplug the power cable of the router and wait for another 30 seconds.
7.Then plug back the power cable and power on your router.
8.Now connect the router to the internet and then to a PC with an ethernet cable.
9.Now launch a web browser on the PC and hopefully, you can access the Routerlogin.net. If so, do not forget to update the firmware of your router to avoid any future issues (Advanced > Router Update).