can't eject network server

i'm using a MBP 2.2 ghz, 16 gb ram, 10.10.5 (i couldn't edit my mac in the link below)

i work in a mostly win pc office, we store lots of files on the pc server, we share files and work form them all day. sometimes, i want to disconnect from the server. i do this by cmd-e or i drag the icon to the trash. sometimes this works, mostly not.

when it doesn't eject, and i have apps open (safari, adobe cc apps, outlook), i'll get an error "the disk "groups" wasn't ejected because one or more programs may be using it. to eject the disk immediately, click force eject button". clicking that button doesn't work.

when i quit all apps, same error result. when i log out and in, same error result. when i open an indesign file that has links to server files, it says the links are missing, so i don't really think the server is still connected, just the icon that won't go away.

when i re-start the mac, the screen goes black, i see the spinning wheel, and i have to force it to re-start w/ the keyboard button.

any solutions or pointers? thanks for your time.