K-knudsen,
Do you have the "Show pre-released versions" option selected (check box at bottom of Stardock Central window)?
If you only purchased WindowBlinds, and not "Object Desktop" - then the failure to update to WB5 beta earlier (and it's not showing now) is due to the fact that WB5 beta is only available to Object Desktop subscribers - as mentioned by Bichur in comment #1.
If you purchased Object Desktop, have you registered your Object Desktop product using "Stardock Central > Tools > Register Products"?
For a mini tutorial on installing Object Desktop, you can go here http://corkyo.wincustomize.com/Articles.aspx?SID=5463&AID=83625 - it includes the "Registering Products" procedure.
Note - the portion of the mini tutorial that deals with "Settings" is geared towards beginners, and therefore recommends the user deselect the "Show pre-release versions" in the settings configuration - just select this one in your case.
BTW - if you do not have Object Desktop, then any listing for WB5 beta is probably a glitch in Stardock Central - which was either showing the WB5 due to registration information not being available, or some other bug.