I see no boards listed as MS-6541 at MSI but that doesn't surprise me since I also have a mobo from MSI that isn't listed. I assume that they are OEM production for manufacturers. My board is inside an advent 3311 but gets a post message from Hewlett Packard
There are several boards labeled 645 on the site so maybe you could check them out to see which one resembles best your board.
go to the link and at the bottom of the page is a search button. type in 645 and see what they give you.
http://global.msi.com.tw/index.php?f...1&maincat_no=1