Just as a reminder, the end of general support (EOGS) for both vSphere 5.0 and vSphere 5.1 is approaching on August 24th 2016.
This, hopefully, isn’t news to anyone currently running these versions of vSphere as VMware maintains a comprehensive public list of products and their EOGS in the following PDF. VMware Lifecycle Product Matrix
What does this mean?
Firstly, it does not mean you are unsupported!
It means that vSphere 5.0 and vSphere 5.1 will no longer receive maintenance and update releases, new hardware support, new guest support, and more.
Review the following link to the VMware Lifecycle Policies for more detail.
vSphere 5.0 and vSphere 5.1 will enter a Technical Guidance Phase and as quoted by VMware means the following:
Technical Guidance is available primarily through the self-help portal and telephone support is not provided. Customers can also open a support request online to receive support and workarounds for low-severity issues on supported configurations only.
VMware Support will continue to support environments running vSphere 5.0 and vSphere 5.1 during the Technical Guidance Phase but it is important to note that no new bug fixes will be issued for these versions and upgrading to either vSphere 5.5 or vSphere 6.0 may be required to completely resolve an issue.
There is no immediate need to rush into an upgrade but it should be something you might want to start planning in the near future.
have you tried reinstalling? 