Cannot bring back some minimized windows

[LutraMan]

I have a new installation of Ubuntu 12.04 that came with Unity.

On the left panel I have links for apps. When I start the app, it gets a small triangle to its left indicating that it's activated.
Some of the apps I've started have changed the triangle to an empty triangle, they are still on, but clicking on the icon now does nothing. If I haven't minimized them I can still get to them by moving the other windows to see them beneath them, but if I'd already minimized them, I have no idea how to get them back.

Can anyone explain this behaviour?

[JohnnyComeL8ly]

I haven't used Unity for a while, but you can try [Alt + Tab] to switch between open windows. If you know the name of the app that is acting up, for example: "crazyapp2;" then try this in a Terminal [Ctrl + Alt + T]

pkill crazyapp2

Now, if you don't know the name of the app, you can try

ps -A

in the terminal and get a good guess as to which one(s) on the list you would like to kill. For example:

me@mymachine: ~$ ps -A
PID TTY          TIME CMD
    1 ?        00:00:03 init
    2 ?        00:00:00 kthreadd
    3 ?        00:00:52 ksoftirqd/0
    5 ?        00:00:00 kworker/0:0H
    7 ?        00:00:14 rcu_sched
    8 ?        00:00:00 rcu_bh
    9 ?        00:00:00 migration/0
   10 ?        00:00:01 watchdog/0
   11 ?        00:00:01 watchdog/1
   12 ?        00:00:00 migration/1
   13 ?        00:22:07 ksoftirqd/1
   15 ?        00:00:00 kworker/1:0H
   16 ?        00:00:00 khelper
   17 ?        00:00:00 kdevtmpfs
   18 ?        00:00:00 netns
   19 ?        00:00:00 writeback
   20 ?        00:00:00 kintegrityd
   21 ?        00:00:00 bioset
   22 ?        00:00:00 kworker/u9:0
   23 ?        00:00:00 kblockd
   24 ?        00:00:00 ata_sff
   25 ?        00:00:00 khubd
   26 ?        00:00:00 md
   27 ?        00:00:00 devfreq_wq
   30 ?        00:00:00 khungtaskd
   31 ?        00:00:02 kswapd0
   32 ?        00:00:00 ksmd
   33 ?        00:00:01 khugepaged
   34 ?        00:00:00 fsnotify_mark
   35 ?        00:00:00 ecryptfs-kthrea
   36 ?        00:00:00 crypto
   48 ?        00:00:00 kthrotld
   51 ?        00:00:00 scsi_eh_0
   52 ?        00:00:00 scsi_eh_1
   53 ?        00:00:00 scsi_eh_2
   54 ?        00:00:00 scsi_eh_3
   77 ?        00:00:00 deferwq
   78 ?        00:00:00 charger_manager
  129 ?        00:00:00 scsi_eh_4
  130 ?        00:00:07 usb-storage
  131 ?        00:00:00 kpsmoused
  139 ?        00:00:02 jbd2/sda1-8
  140 ?        00:00:00 ext4-rsv-conver
  261 ?        00:00:00 upstart-udev-br
  267 ?        00:00:00 systemd-udevd
  299 ?        00:00:00 cfg80211
  315 ?        00:00:00 kworker/u9:1
  442 ?        00:00:00 upstart-file-br
  513 ?        00:00:01 rsyslogd
  555 ?        00:00:00 upstart-socket-
  634 ?        00:00:52 dbus-daemon
  672 ?        00:00:00 ModemManager
  692 ?        00:00:00 bluetoothd
  701 ?        00:00:00 systemd-logind
  726 ?        00:00:00 cupsd
  727 ?        00:00:00 krfcommd
  782 ?        00:01:22 NetworkManager
  833 ?        00:00:00 polkitd
  891 tty4     00:00:00 getty
  896 tty5     00:00:00 getty
  900 tty2     00:00:00 getty
  901 tty3     00:00:00 getty
  905 tty6     00:00:00 getty
  937 ?        00:00:00 cron
 1000 ?        00:00:34 irqbalance
 1044 ?        00:00:00 lightdm
 1049 ?        00:00:20 wpa_supplicant
 1078 tty7     00:23:38 Xorg
 1081 ?        00:00:00 accounts-daemon
 1105 ?        00:00:01 whoopsie
 1121 ?        00:04:50 mysqld
 1138 ?        00:00:03 dnsmasq
 1307 ?        00:00:13 apache2
 1354 ?        00:00:00 kauditd
 1551 ?        00:00:00 timidity
 1557 tty1     00:00:00 getty
 1606 ?        00:00:00 lightdm
 1618 ?        00:00:00 init
 1677 ?        00:00:00 dbus-launch
 1679 ?        00:00:00 dbus-daemon
 1691 ?        00:00:07 dbus-daemon
 1694 ?        00:00:00 ssh-agent
 1699 ?        00:00:00 upstart-event-b
 1720 ?        00:01:15 ibus-daemon
 1733 ?        00:00:00 upstart-file-br
 1734 ?        00:00:01 lxsession
 1737 ?        00:00:04 upstart-dbus-br
 1739 ?        00:00:08 upstart-dbus-br
 1742 ?        00:00:00 gvfsd
 1747 ?        00:00:00 gvfsd-fuse
 1756 ?        00:00:00 ibus-dconf
 1757 ?        00:00:31 ibus-ui-gtk3
 1759 ?        00:00:26 ibus-x11
 1763 ?        00:00:00 at-spi-bus-laun
 1767 ?        00:00:00 dbus-daemon
 1770 ?        00:00:00 at-spi2-registr
 1782 ?        00:00:16 ibus-engine-sim
 1797 ?        00:00:22 openbox
 1800 ?        00:00:54 lxpanel
 1801 ?        00:00:36 pcmanfm
 1808 ?        00:00:00 ssh-agent
 1823 ?        00:00:00 menu-cached
 1830 ?        00:00:02 gvfs-udisks2-vo
 1836 ?        00:01:04 udisksd
 1846 ?        00:00:00 gvfs-afc-volume
 1851 ?        00:00:00 gvfs-gphoto2-vo
 1855 ?        00:00:00 gvfs-mtp-volume
 1865 ?        00:05:59 pulseaudio
 1867 ?        00:00:03 rtkit-daemon
 1871 ?        00:00:00 gconfd-2
 1874 ?        00:00:00 gvfsd-trash
 1890 ?        00:00:00 gvfsd-metadata
 2008 ?        00:00:00 xfconfd
 2758 ?        00:00:00 gvfsd-http
 3190 ?        00:00:00 console-kit-dae
 4035 ?        00:01:15 nm-applet
 4053 ?        00:00:00 gnome-keyring-d
 6380 ?        00:00:00 upowerd
 7080 ?        00:00:00 kworker/1:0
 7249 ?        00:00:07 gnome-terminal
 7253 ?        00:00:00 gnome-pty-helpe
 7254 pts/1    00:00:00 bash
 8035 pts/1    00:00:00 nano
10321 ?        00:00:02 kworker/1:2
10344 ?        00:00:00 dhclient
10452 ?        00:00:06 ntpd
10481 ?        00:00:07 kworker/0:0
12165 ?        00:00:00 apache2
12166 ?        00:00:00 apache2
12167 ?        00:00:00 apache2
12168 ?        00:00:00 apache2
12169 ?        00:00:00 apache2
12406 ?        00:00:00 dconf-service
12410 ?        01:44:38 firefox
12449 ?        00:00:00 apache2
12667 ?        00:00:02 kworker/u8:3
12690 pts/3    00:00:00 bash
12718 ?        00:00:02 kworker/u8:0
12721 ?        00:00:00 kworker/0:1
12736 ?        00:00:01 kworker/u8:1
12744 ?        00:00:00 kworker/u8:2
12747 ?        01:14:57 crazyapp2  <fictitious: only for example>
12758 pts/3    00:00:00 ps

You can now also use

kill 12747

instead of

pkill crazyapp2

because you know the PID of the app.

I hope this helps you; if not, ask me more.

P.S. I had the same problem in Unity, but now I use LXDE because my olde PC won't keep up (I can't say what your problem is for sure).