How to connect to a virginmedia router

i don't want to set up another network with the time capsule

When you set up the Time Capsule, the basic default settings will create a wireless network on the TC. You can always turn off the WiFi on the TC once it is set up if you don't need a second network for your "guests" to use......so you don't have to give them the password for your "private" network.

i don't want to set up another network with the time capsule

The Time Capsule must connect to another router using a permanent wired Ethernet cable connection. Or......

If you cannot run the Ethernet cable, then you might be able to to use a pair of Ethernet over powerline adapters to send the signal over the existing AC powerlines in your home. In other words, the theory with these devices is that you already have the wiring in place, you just need the adapters.

i would like to use the ethernet port on the TC to connect to a Blue-ray player which the TC will be sat on top of.

That will be no problem if you connect the TC back to your main router using a permanent wired Ethernet cable connection or via Ethernet over powerline adapters.

If you have a spare AirPort Express, it might be possible to configure the AirPort Express to wirelessly "join" the network that your main router is producing. When the Express is configured this way, the Ethernet adapter is enabled, so you could connect the TC to the Ethernet port on the AirPort Express and theoretically set up the TC that way.

Note...... I'm not recommending that you do this, simply pointing out that it is an (unusual) option. You would need either the A1264 or A1392 version of the AirPort Express for this task.

Any idea why i can't use the ethernet ports though?

Apple disabled the Ethernet ports when the TC was set up to "join" a network....for good reason. Things are already "iffy" with "double hop" wireless and adding more devices to the TC slows things down even further, with even more chances for problems.

You had specified in your original post that you planned to connect additional devices to the TC via Ethernet. My answer assumed that you wanted to have this capability.

It is a used 500gb

This would mean that you have a version of the Time Capsule that is at least 9+ years old and likely older, so hopefully the previous owner has replaced the power supply and hard drive on the device.

The TC can be located anywhere that you want, as long as it is connected to your main router or modem using a wired Ethernet cable connection, or using another Ethernet connection option.

The Setup Guide for the Time Capsule is very clear on this. Please note the example below from the Setup Guide.

Nice work. You had to use an old version of AirPort Utility to do this, and I assumed that you were not using a 7+ year old version. My mistake for assuming anything.

If things work OK, that is great. But......you now have what is known as a "double hop" situation. To back up to the Time Capsule, your the signal from your Mac must travel over WiFi from the Mac back to your main router......hop one.....and then the signal must travel from your main router to the Time Capsule over WiFi......hop two.

That means that backups will take twice as much time to complete and there will be twice as many chances for an error to occur in the process. It's the worst possible way to set up backups to a Time Capsule.

This is the reason why Apple removed the "join" option for the Time Capsule starting with the Mountain Lion operating system in Macs about 7 years ago. Too many problems with the "double hop" setup.

But, if things seem to work OK for you, that is great. You may be one of the lucky ones.