By the sound of it, your system lost the whereabouts knowledge of the BOINC data directory [corrupted or emptied or loss of access rights etc]. Doing reinstall will not have improved the chance of recovery without proper method. First things first, find the BOINC data directory. Assuming you're running the official WCG client 6.10.58 and Windows, (which?), the data dir could be in the user area or in default places such as C:\ProgramData\BOINC. Without system information / client version, there's no giving more precise directions. An uniinstall and then a new install pointing the client at the data directory where your old data was may help the chance of recovering the previously known client. Have my doubt though... as in too late.

*Latest* in BOINC world is a really vague term.. the BOINC Manager Help About box and BM advanced view right bottom says what version it is exactly. Then knowing if user install or "Protected Application Execution" aka service install also makes a difference, but for W7, I'd expect the data dir to be C:\ProgramData\BOINC. If reinstalled without backup, the new install will have done the damage... old data lost... chance of old client install rock bottom.

Are there in the one with the 53 files more sub directories such as slots/ or projects/ and a file for instance named stdoutdae.txt or client_state.xml [in that program files(x86)/BOINC folder]? If so, you're in trouble [violating some W7 security rules]. Windows *hates* live data / frequent written to files such as for BOINC be in the program files and program files(x86) folders.

Default, BOINC 6.10.58 just won't install any data files into the base program files folder.... they go either to a user area or the noted C:\ProgramData\BOINC. How they got in C:\Program Files(x86)\BOINC... you tell me, cause I dont and as you noted, your other client does fine. You can check there for the BOINC data directory in the path I gave.

On the problem device, plz check in file explorer if there is also a BOINC directory in C:\ProgramData. The folder could be hidden, in which case you can type the address in the location bar at top of explorer. Usually as you type, W7 will offer to complete the address from the list of folders it knows.

This is the fasttrack to getting running again, possibly with your old client [noguarantees]

1. Uninstall BOINC, [rerun the installer and select uninstall].
2. Install BOINC, whilst following this FAQ item 4 http://www.worldcommunitygrid.org/forums/wcg/viewthread_thread,28971.
3. When getting to the second frame in the screenshot, make sure the Data Directory path is C:\ProgramData\DATA. If not amend.
4. In that same frame 2, select Protected Application Execution which makes BOINC run as a service, and select "Allow all users" (Read all the red text carefully).
5. Do Next and proceed to install.

Let us know what's happened (for now don't worry about the extra files).