Trouble connecting to internet

Hope I can get some help here and my problem is not too long and confusing.

My main router provided by my isp is on the first floor of my house and I ran a cable up to the third which I then connect to an asus router and in turn is connected to my desktop. I have used this set up for the past 1 1/2 years or so with no issues.

When I turned on my desktop yesterday, I was not connected to the internet although my other devices were still connected to the wifi.
Restarted a couple of times and nothing happened.
Did some googling and use command prompt to do some ipconfig commands and everything was fine.

Later that day, when I turned my desktop back on, I had no internet again and this time the same method did not work. tried a couple of other solutions I found online as well as resetting and reconfiguring the router again but it did not work either.
I connected the ethernet cable to an old laptop just to test if it was my desktop problem but I couldn't get a connection as well, although it could connect thru wifi.

I decided to try connecting my desktop directly to the lan point in the wall (which runs from the isp given router) and it worked after a restart. However, since then I have had to restart my computer several times before I get a connection.

a couple of hours ago, my isp sent some one over to check out my problem. he suspects it is something to do with my desktop which it probably is as he has no problem when connecting his laptop to it and I have also tested on my mac and a newer laptop without any problems.

hopefully it isn't difficult to understand and sorry if the post is long.

thanks in advance!
 
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