Google Drive system tray icon gone

Yes, I too suffered from the same problem. You have to check three things:

1. Make sure that you have installed Google Drive latest version properly.
2. The Google Drive icon will appear in your system tray (notification area). Right click to open the folder. If it does not appear, follow step 3.
3. Make sure that you are in the Administrator account or if you are in a normal user account check whether your folder (account name in C:\Users) in public mode.

The solution of @pestul didn't work here. Even with diagnostics mode (C:\Program Files\Google\Drive>googledrivesync.exe --vv), the app failed to start.

So I deleted the C:\Users\*username*\AppData\Local\Google\Drive folder and the app started again. Of course you will have to re-enter your credentials and start the whole sync process from the beginning BUT the new GoogleDrive version (1.18.7821.2489) doesn't force you to start with an empty folder, meaning you can point to the old folder AND it now detects if the local files are the same on the server, eliminating the need to synchronize everything from scratch!

As an example, it took approximately less than 5 minutes to synchronize my 13.31GB folder with 60.063 files in it. In the middle of the process it will show a popup window telling you the number of files that exist only locally, the number of files existing only on server, and the number of files conflicting.