Problem: (Windows XP) Can't start programs even though there are current running ones. Menus, buttons, Start button, and other GUI elements disappear.

Error: No error message.
Cause: Window's desktop heap size is too low and Windows run out of resources (too many open windows)
Solution: Increase the desktop heap size

Step 1:  Start -> Run -> "regedit" -> Registry Editor should be opened, go to the folder tree:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\SubSystems
Step 2:  On the right panel of the Registry Editor, there should be a key called Windows (REG_EXPAND_SZ), double click it -> replace everything in Value data with:
%SystemRoot%\system32\csrss.exe ObjectDirectory=\WindowsSharedSection=1024,8192,512 Windows=On SubSystemType=WindowsServerDll=basesrv,1 ServerDll=winsrv:UserServerDllInitialization,3ServerDll=winsrv:ConServerDllInitialization,2 ProfileControl=OffMaxRequestThreads=16 or in the SharedSection=1024,3072,512 part, change the value 3072 to 8192 -> OK and restart for it to take effect.

Sources: msdn.com, pcreview.co.uk, techguy.org
Keywords: buttons disappear, blank menu, can't start programs, can't run programs, cannot start programs, cannot run programs, programs won't start, programs won't run, programs won't open