Internet speed too slow when not directly connected to router

[CAPSONLY420]

Hey guys,
a few weeks ago I moved and got my new internet connection. Since the router is located in a different room we installed a cable(cat5e) from the router over the attic into my room. For the first 2 weeks I got the full internet speed(200mbit down/10mbit up), since about 2 weeks ago I only get about 50-70mbit down speed.
I tried connection different PCs to the network outlet in my room and all of them only get the 50-70mbit. Then I connected the same PCs directly to the router and I got the full speed.
The confusing part to me is that it work fine at the beginning and then all of a sudden it didn't.

Before I go and pull out the entry cable and network outlet and install a new one I thought I'm gonna ask if someone here can help me.

 

[BadAsAl]

Only thing I can think of is the cable somehow got damaged or is getting interference in the attic. Can you get another cable and try that without going through the attic? If that fixes it then it must be something with the original cable.

 

[CAPSONLY420]

Only thing I can think of is the cable somehow got damaged or is getting interference in the attic. Can you get another cable and try that without going through the attic? If that fixes it then it must be something with the original cable.

Alright, so I did exactly what you said, I disconnected both network outlets from the cable that goes through the attic and connected them to a cable that i just ran through my apartment and everything worked perfectly.
So i connected the network outlets back to the cable that is running through the attic until i could get a new cable and now everything works perfectly.
I still have no idea what the problem was but it works so I'm satisfied.