In order to return the list of computers, the Web Console will submit a Web Services API request. Web services will route the requested info via AM Object Manager for AM related items, and and SD API server, for SD related items.
We would need to see a ZIP of the logs from the DM, in detail mode, to determine the following:
1- Does the web service trace show the web service methods being called, and returning an error. If so, is this error in the usage of the web service request, or did one of the ITCM components return an error back to web services?
2- If a request was dispatched to AM or SD manager/APIs, did that request return an error.
Going back to Rich's response, your best course of action is probably to open a support case, and attach the detail logs capturing the problem.