G'day from DownUnder and welcome both of you to linux.org
Not correct, I am afraid, the installation of Kubuntu alongside an existing install of Windows should have generated a Grub Menu, which would appear on reboot, showing Kubuntu at the top, then advanced options and followed by a line mentioning Windows Boot Manager.
Something has not worked correctly.
@Korhan , depending on whether your computer is BIOS or UEFI
In your Kubuntu, you could also give us the specs for your computer as follows.
1. Install the package inxi
Then issue the command
and copy and paste the output of that into Code fields here as the picture shows below.
2. Also please give us the output of
I will try to get back to this Thread as soon as I can, but others may be along.
Cheers
Chris Turner
wizardfromoz