You could begin by looking at your startup programs. Run System Configuration and click on the Startup tab.

I tried that and have only three things checked for start up.

1. Install Shield Update Service

2. Microsoft Intelli Type Pro

3. Microsoft Windows Operation System

Am I missing something that should be checked?

Thanks,

Kate 

Try unplugging any external devices except your keyboad and mouse and monitor.

Also list your system model and OS 

Did you do a repair or upgrade of Vista recently?

 Yes I did a Update.

Windows Vista Ultimate Service Pack 1 

Processor: Intel (R) Core (TM) 2 CPU 6400@2.13 GHz  2.13GHz

Memory (RAM) 2.00 GB

System type: 32-bit Operation System

IVI Virtual CD SCSI CdRom Device

TSST corp DVD+RW TS-H653A ATA Device

 

You done an update or upgrade?

A Windows update.

I am suprised by how short your list of start-up items is and I don't see anything that stands out. I would uncheck the Install Shield Update Service as a precaution against viruses, etc.