Here are some steps you can follow (It assumes that you have ASP.NET extension allowed in IIS mmc Web services extensions and your ASP.NET works — you can check event logs for possible errors):

1. Try Plesk Reconfigurator (Start->All Programs-SWsoft->Plesk Reconfigurator-> Repair Plesk installation->check File Security)
2. If above step has not helped:
Start->Run->cmd
cd %plesk_dir%
websrvmng –remove-vhost –vhost-name=your_domain_name_which_doesn’t_works
________________________________________
check for errors if they are present post their description here
________________________________________
websrvmng –reconfigure-vhost –vhost-name=your_domain_name_which_doesn’t_works
________________________________________
check for errors if they are present post their description here
________________________________________
3. If above steps haven’t helped:
a).In IIS mmc right click domain -> Click Properties->Click Directory Security Tab->Click Change
b).Ensure that anonymous access is selected
c). Ensure that IUSR_domain_user account is selected for access
d). Ensure that Windows integrated authentications is selected

4).
a).Click Start-> My Computer
b). type %plesk_vhosts%->click enter
c). Right click domain-> Click Sharing and Security-> Click Security Tab-> Click Advanced
d). Ensure following ACL schema is applied:
(Note: Domain user is an account you’ve created for domain user to access ftp)
_________________________________________
Administrator Full Control not inherited for this folder,and subfolders and files
System Full Control not inherited for this folder,and subfolders and files
Domain user Read not inherited for files only
Domain user Read and Execute not inherited for this folder,and subfolders
__________________________________________
e) Double click domain-> Right click httpdocs-> Click Sharing and Security-> Click Security Tab-> Click Advanced
f). Ensure following ACL schema is applied:
__________________________________________
Administrator Full Control not inherited for this folder,and subfolders and files
System Full Control not inherited for this folder,and subfolders and files
Domain user Full Control not inherited for subfolders and files
Domain User Special not inherited for this folder only (will be detailed later)
Plesk IIS WP USER (Machine\IWAM_application_pool) Read not inherited for files only
Plesk IIS WP USER (Machine\IWAM_application_pool) Read and Execute not inherited for this folder,and subfolders
Plesk IIS USER (Machine\IUSR_domain_user) Read not inherited for files only
Plesk IIS USER (Machine\IUSR_domain_user) Read and Execute not inherited for this folder,and subfolders
FPSE_xxxxx(Machine\FPSE_xxxxx) Read not inherited for files only
FPSE_xxxxx(Machine\FPSE_xxxxx) Read and Execute not inherited for this folder,and subfolders
_________________________________________

(Note: the last two permissions present only if you have MS Front Page allowed for domain)
_________________________________________
Domain User special permissions set to allow
Traverse folder/execute files
List Folder/ Read Data
Read Attributes
Read Extended Attributes
Create Files/Write Data
Create Folders/Append Data
Read Permissions
__________________________________________
5. If above two steps in addition to previous steps have not helped:
a). Right click My Computer->Click Manage
b) Double Click Local Users and Groups
c) Click Users->In right pane right-click IUSR_domain user->Click reset password->type desired password ->click OK
6. If above steps have not helped.
a).Backup Domain using Plesk backup (Start->All Programs-SWsoft->Plesk backup->Ensure only that one domain checked-> Click Start) Ensure domain successfully backed up!!!!!
________________________________________
check for errors if they are present post their description here
________________________________________
b).Remove domain from Plesk (If you have external SQL databases ensure you know db user password, also write down any DSN created for domain)
c). Restore domain from backup (Start->All Programs-SWsoft->Plesk restore-> select backup for domain->select by domains option-> Click next-> Ensure domain binded to right IP-> click next-> Ensure Keep current key option selected-> If you have MSSQL database enter user login and password-> Click Start
d) Restart IIS