There could be a lot of possibilities for this issue.

I hope one of the following solutions could help you out.

1. Check that the Act! addin is still active.

To check this follow the steps in your Outlook.

Go to Files->Options->Addins.

their should be a list of all add-ins you´ve installed.

Search for the "Act! Outlook Add-in"                          

                                                                               -> If the Addin listed under "Inaktive Appliance Add-Ins" go to step 1.1.

                                                                               -> If the Addin listed under "Disabled Appliance Add-Ins" go to step 1.2.

                                                                               -> If this two steps wont help jump to step 2.

                                                                               -> If your addin always jump back to inativ or disable please go to step 3.

1.1. How to move a Outlook Add-in from inactive to active:

At the bottom of the window you can see the drop down menu "Manage" you have to choose "Com Add-Ins" and press "Go..."

After pressing "Go..." a little window pops up please set the tick mark at the "ACT! Outlook AddIn" and press OK

1.2. Activate disabled Addins for Outlook:

At the bottom of the Addin list window you can see a drop down menu "Manage:" here please choose the option "Disabled Items" and press "Go..."

Then a littel window shown up. Now select the Act! addin and press Enable.

If it´s done the Act! addin often jumpes to inactive to change it to active go to step 1.1.

2. Outlook service startup:

Check if you run outlook on startup to see that follow this steps:
Press "Windows button" + "R"
Type in "msconfig" and press ok.

Now make sure that the three marked points are selected, if not select them.

If Outlook is listed, uncheck it if its already selected.

If you have done some changes, you need to click ok and confirm the notification. Then restart your computer.
Check if the Act-addin has loaded now.

If your Act-Addin get disable all the time by itself please follow this link.

 3. Registry based Solution help if your addin won´t get back to activ


Make sure outlook and Act! are closed when you perform these steps.


3.1. Press Windows button + R, write "regedit" and click run.
Now the Registry-Editor should open up.

Important:

(Before you do this steps, it would be good to do an backup of the registery.)
(How this is done, is shown here).

 

3.2. Select the path ""HKEY_CURRENT_USER\Software\Microsoft\Office\15.0*\Outlook\Resilienc\DisabledItems"
*(the number 15.0 is set if you use offic 2013 if you use another office its another number)

here you need to select the "REG_BINARY" Typ and delete it.

Important if you do this you aktivate all Addins so please get sure you know which one was disabled.

 
Now please check if your Addin is back to aktiv now and you could use the Act icons again.