Hi Sandrine,

There are some general reasons as to which your StrongVPN connection is not working which I have described below along with the troubleshooting you need to do.

Fix 1: Software Firewall :

The easiest way to test if it's conflicting with your VPN connection is to disable it and try the connection again.
If this allows you to connect to the VPN you'll need to setup an exception in order to use the VPN while it's running.
This will vary depending on your firewall software, but in general you will need to allow outgoing connections to port 1723.
Alternatively you could set an exception for all traffic to the VPN server address.

Fix 2: Check your Router

It's possible your router doesn't support or isn't configured for PPTP VPN Pass through.
To test this, try connecting to the Internet without the router and see if it works. In other words plug your computer directly into your modem device bypassing the router.

Fix 3: Error in Creation  

This one is odd but it does happen. For whatever reason sometimes the second time when you create a VPN connection it will work. So delete your first one, and try again. 

Then Reboot as System resources can run low and cause all sorts of problems. Try to reboot your PC, Router, and Modem, then once the PC returns start VPN before opening any applications (Skype, browser, etc.)

Fix 4: Your Current Location

You may be in a country or with an ISP that blocks PPTP VPN connections, such as Oman, UAE and others.
If so it's possible your ISP is blocking, check with your friends and see if they confirm this. Another option would be to contact your ISP directly to ask.

Fix 5: Copy password correctly
Also check while entering in the password, make sure there is not a space at the end, since when you copy/paste the password sometimes a space is added at the end and that password will not be accepted


Fix 6: Check date and time of your machine
Check your computer time. If your date or year is off or not correct, this can actually cause quite a few problems. Check to make sure your Time and Date are accurate.

Fix 7: Change protocol of your VPN

If you are on a OpenVPN account, there are many possible configurations and these changes can have a positive effect.

• Try to Change Protocol from UDP to TCP (Default is UDP).
• On the OpenVPN software side try a different version. Sometimes the latest version does not work as well as an older one.

I hope this helps in getting you connected to your VPN.

Regards,
Lokesh