First make sure to restart your computer after installing Sylenth1. Also make sure that you have installed the latest version of Sylenth1. Then activate and rescan the VST and AU plug-ins list in your host software's preferences.

If you're using Logic Pro X, select "Preferences" -> "Plug-In Manager" from the Logic menu. Then select "LennarDigital" -> "Sylenth1" and click "Reset & Rescan Selection".

If you're using Ableton Live, make sure to force a full rescan of all plug-ins by holding down the Alt/Option key while clicking the "Rescan" button in Live's Preferences.

If Sylenth1 still doesn't load, try resetting its file permissions. Open Terminal from Applications/Utilities, then type:

sudo chmod -R 775 /Library/Audio/Plug-Ins/Components/Sylenth1.component
sudo chmod -R 775 /Library/Audio/Plug-Ins/VST/Sylenth1.vst

And enter your password when asked for. After that rescan the plug-ins in your host software.

To activate Sylenth1 please follow these instructions step by step.

The soundbanks are located in the Sylenth1 data folder. Just click MENU -> "Open Data Folder.." in Sylenth1 to get there quickly.

It is important to always deactivate Sylenth1 before removing it! Click MENU -> Deactivate in Sylenth1 to do so.

Sylenth1 stores soundbanks and preferences in the Sylenth1 data folder. To quickly get there click MENU -> "Open Data Folder.." in Sylenth1. Then delete this folder. After that delete these two files from your main drive in OSX:

/Library/Audio/Plug-Ins/VST/Sylenth1.vst
/Library/Audio/Plug-Ins/Components/Sylenth1.component

If you're not sure how to get there, open Finder, select 'Go' from the top bar menu and click 'Go to Folder..'. Then type '/Library/Audio' and click 'Go'. Now browse to the corresponding folders and delete the files.

Sylenth1 responds to MIDI Program Change and Bank Select messages, which are used to switch the preset to a certain number. Most MIDI keyboards/controllers can send these messages so you can easily change presets directly from your controller, without touching your computer keyboard.

These messages can also be recorded in a MIDI track. When you import or record a MIDI track that contains a Program Change message, Sylenth1 will switch the preset whenever it reads the message. So just make sure to remove the Program Change or Bank Select messages from the MIDI clip if you don't want it to change!

Check your host software's user manual on how to remove or edit Program Change and Bank Select messages in a MIDI clip. If you're using Ableton Live, make sure the Pgm, Bank and Sub fields in your MIDI clip are all set to None.

Alternatively, you can completely disable Program Change messages in Sylenth1. To do so, click MENU -> "Open Data Folder..", browse to Config and open the Settings.xml file with a text- or xml-editor. Change the "programchanges" value in the MIDI section to "0" and restart Sylenth1.

Click MENU -> "Check for updates" in Sylenth1 to find out if you're using the latest version of Sylenth1. If not, download it from the links in your license email and install it.

If you're running a 32bit host program, Sylenth1 may show up as a blank window on macOS 10.12 Sierra. In the switch to 64bit computing, Apple deprecated some of the old 32bit Carbon code in Sierra. This may cause some 32bit plug-ins not to work correctly.

To fix the problem, just make sure to run your host software in 64bit mode. If you absolutely need to run it in 32bit mode, you should downgrade to and older version of OS X.