SYMPTOMS
when using a program such as Notepad that uses common dialog boxes and clicking Open on the File menu and then click the drop-down arrow on the Look In box or the Save In drop-down box in the Save or Save As dialog boxes, you may experience a problem that takes several minutes before the lists actually drops down.
That are some reasons for that delay: 1) if you have persistent connections to network drives (for example, to drive Z) that are inaccessible for some reasons, 2) if you are working offline with no network connection.
RESOLUTIONS
1) If opening windows explorer take a long time also, make sure all network connections are active. If not, disconnect no accessible network drives.
2) To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix.
3) Instead of connecting a persistent network drive to a network location, add the network location to My Network Places.
4) Instead of connecting a persistent network drive to a network location, use logon script to map the network drive with /persistent: no option. Refer to MS Q321126.