Lost synced contacts in my HTC Desire HD
You may need to re-enable syncing of your Google contacts. Here's a simple guide on how to do that: http://www.wikihow.com/Sync-Google-Contacts-With-Android.

Also, the contacts may be on your phone, but not set to display. To fix this, go into your contacts list, hit the menu/options button, and open "Contacts to Display". Make sure that your gmail contact list is enabled in this menu.

Finally, if those don't work, check this link: https://productforums.google.com/forum/#!topic/gmail/zCWHBp5d9h4