I was using windows 10 and then I did a dual boot with ubuntu 16.04 and used this as it is for months but afterward dual to some hardware problem(screen display) I gave my laptop to a service center to fix it but after getting back my system is only showing windows not ubuntu. Is there anything that we can do recover ubuntu.
while bootloading(before showing the Windows logo), try keep pressing left shift button. if Grub is there it will load the grub. If grub loaded then you can access Ubuntu or boot with advanced options and fix broken packages. else you have to manually install grub.