My Dell 1545 locks up after 30 minutes of use. It will not do a complete shut down, gets stuck at log off. Screen will say it is logging off for over an hour if I let it.
It will not take the auto updates. It tries and fails on updates.
Anyone have any ideas on this?

All right, I ran the virus scan. No virus' detected.
Turned off the firewall and virus protection to download malwarebytes.
Ran malwarebytes and found nothing.
Did a clean startup and my problem with the locking up did not happen. The machine ran fine through all the restarts.
I turned everything back on (normal start, virus and firewall) and then the computer locked up. After it locked up, I tried hitting control-alt-delete, and going to shutdown from there. Screen became somewhat dark and after a few minutes I got the following message;
"Logon process has failed to create the security options dialog.
Failure - Security Options".
Any suggestions?
Thanks for your help.