Without knowing what model or firmware version, I can only provide with very limited recommendations:
1- Verify that your thin client has the latest firmware installed available at: https://appservices.wyse.com/pages/serviceandsupport/support/downloads.asp
2- Verify that your thin client has the latest BIOS version installed at the same link as above.
3- Verify that the client/receiver is installed for the infrastructure you have (Citrix, VMware, Microsoft)
If this does not resolve your issue, please include the model and version of the OS you have installed and what error message you are getting.
Imaging of Dell Wyse thin clients is done via the USB Firmware tool, or Wyse Management Suite. You can download the USBFT and documentation from the following url: https://downloads.dell.com/wyse/USBFT/3.1.0/