Yesterday one of my computers had a system crash, and the filesystem containing the BOINC data directory was corrupted. Windows performed an automatic chkdsk on the volume, and rearranged things a bit, including putting 3 BOINC data files in a "found.000" directory.

When BOINC restarted, the boincmgr task list was empty, as was the messages list. Most menu options were greyed out. I could get a message saying that it (boincmgr) could not find a client (I forget how). boinc.exe was not in the task manager processes list.

I killed boingmgr and boinctray and then tried copying the one rescued orphan file that was not already there back into its slot directory, and started boincmgr again. The problem remained. I saved a snapshot of the BOINC data directory, then uninstalled and reinstalled BOINC. This left just a handful of new files in the BOINC data directory. I deleted these, then copied my snapshot files in. No go. I uninstalled and reinstalled BOINC a second time, and attached to WCG anew. Crunching for WCG was up and running again.

I was unhappy about losing the tasks in my work queue, expecting them to time out after their deadline. I need not have worried, as they have all been deemed "Detached", probably when I reattached the new BOINC installation to WCG. They have been re-sent, and some have been validated for their new owners already.

I've been around computers and WCG/BOINC for some time now, and found a way of dealing with this situation. However, less experienced or less motivated people may not have rescued it, and they may have dropped out of contributing to WCG. It wasn't a "user-friendly" situation, and I thought you should know.

BOINC 6.2.19 32-bit, Windows XP-64 SP2.

I haven't looked extensively at the BOINC log files, but stdoutdae.txt did not have anything useful. I still have the data snapshot, in case someone wants it.
The machine is overclocked, but it has never before crashed in this manner. There was a very brief mains power dropout (unusual) at about the time of the crash, and that may have been the trigger.