The most common reason for a slow desktop is internet connectivity. Run a speed test from your computer. Copy this URL: www.bandwidthplace.com and visit the website from your computer. Report the results to support. We recommend bandwidth of 1MBps or more per user and latency under 100ms.
Another reason could be that your desktop is tied up by some application such as Outlook, Excel or the browser. For example, you had a large Excel spreadsheet open and its busy calculating a formula. Wait for the application to finish its work.