NAS does not connect to the internet anymore

[lager]

My System:
Terramaster F2-220
4 GB Ram
Firmware: 5.1.67
BIOS/initBoot version 5.6.5

A couple days ago i saw that my F2-220 NAS was shut down - i wondered maybe a power failure in the house the night before.

I run the NAS 24/7 and only as a Plex Server - nothing else.

Since I never ever saw it shut down before i first wasn't worried and i started it and it went up again but then the problems started.

There were no firmware updates on the router nor did i make any network changes and the NAS is directy connected via lan to the router.

First I couldn't login over the webrowser anymore. After a while i figured out what it was.

I had (still have) the "ip issue" instead of the 192.xxx.x.xxx i got an 169.xxx.x.xxx ip.
So i downloaded the "TNAS PC" Software and was able the change the ip to the old one again (but the change is only temporarily i don't know why).

So far - so good. At least i can login over the webbrowser again and well that's about it what i can do.

I opened the app "Plex Server" and could see all my Movies and TV Shows but something seemed odd so i made a couple of changes in my movie/tv show libraries and the next problem appeared. "Plex" didn't connected to the internet to update the changes.
First i thought that due to the shut down of the NAS. So i began to make more and more changes in the settings of "Plex" but nothing happened at all. So i decided to delete Plex completely and install everything new.

Here the next problem appeared in the "App Center" i can see the "Plex" app but i couldn't download it anymore.
Everytime i press install a message pops up "Operation failed.".
So i downloaded the "Plex server" directy from the Webpage to a Win10 Laptop and manually to the NAS. Installation worked fine. Connected it to my movie/tv show libraries but again no connection to the internet to update everything.

So i thought okay let's try the plex installtion via Docker - same issue "Operation failed."

Then i thought okay probably (due to the shutdown) the TOS 5.1 is broken somehow.

I took a new harddrive stuck it in the NAS and initiated an total new install of TOS 5.1 - and i failed.
Same problem as before since it does not connect to the internet i had to download the bootloader and the TOS from the Terramaster webpage to a Win10 Laptop and manually to the NAS - which worked - but again still no connection at all to the internet after the installation.

If i check for updates in the "Control Panel" -> "System" -> click on "check for updates"
A pop up message appears saying: "update check failed. The TNAS is not connectet to the internet."

Since it does not even connect to download the bootloader or the TOS i assume it's hardware failure.

I am total clueless is it a hardware or software issue? I am baffled since i have no problem at all to get on the NAS via a Win10 Laptop where i mapped the drive of the NAS. I have total access to the drive and I can copy, paste, delete, rename any file or folder i want.
Even when it changes again and again the ip to a 169.xxx.x.xxx Number.
No access problems at all. Win10 "remembers" the mapped NAS drive.
I tried "Kodi 21" via Laptop and i made a path to mymovie/tv show libraries and everything works fine so i have total access to the NAS.

I even switched the lan cables and instead of putting it direct in the router i tried it in a switch - same result i got a 169.xxx.x.xxx number again - which means no internet connection.

Okay since all my changes in the system (software and hardware wise) didn't work i know so far that "the" problem is: the NAS can't connect to the internet anymore - but why?

Can it be fixed or do i need a new NAS?

[TMzethar]

Regarding the 169.xxx.x.xxx issue, this is because the PC connected to the NAS does not have a DHCP server and cannot be assigned an IP.
For details, please refer to:viewtopic.php?t=1224

Regarding the TOS5 system issues and installation failure you encountered, it may be from the limitation of TOS4's storage structure.
For details, please refer to:viewtopic.php?t=4912

[lager]

i fixed the problem - well actually i found the solution (but i still don't know what caused the problem in the first place).

This post helped me: viewtopic.php?t=5939

I turned off the DHCP option and put in the ip manually and since then everything works perfect again.

So you can close and/or delete my post.