Dell workstation performing slowly

Since you say its a Dell machine I whould:
1. Contact Dell and ask them, they are very helpful.
2. Dell always gives you a CD-ROM (among the other CDs) with the computer that has Diagnostic tools on it, Those are very usefull to troubleshoot hardware problems. It does a complete scan of all your hardware, including memory and harddrive. I think you should try this because from what you describe it looks like a Hardware problem and not software. I whould however also try to reinstall every thing and not install any progrmas that run in the background, and if you don't have the same problem than the problem is with the software thats running in the background, so I whould then look for any updates for that program.

click on start --> run and type msconfig

click on selective startup --> startup

and remove those items oone at a time until resoures are freed up.

The slow performance eould be due to low in system resources. The system resources problem can be solved by using the MSCONFIG utility, deleting Temporary files, or performing hard disk maintenance.

MSCONFIG is a utility that allows you to configure which programs will start when you start up the computer. By eliminating selected programs from startup, your computer will have more resources for multitasking. You can still run the programs by accessing them from the Start menu.

To run MSCONFIG, follow these steps:

1. Click Start, and then Run.
2. Type "msconfig" and press Enter.
3. Click the Startup tab.
4. Clear the checkboxes for programs that you do not want at startup except do not clear the boxes for systray and scanregistry. Systray displays the time and other icons for applications running in the background. Scanregistry makes backup copies of the registry that can be restored if a software installation corrupts the registry.
5. Click Apply and then click OK.
6. Restart the computer.
7. The desktop may look different and you may lose some functionality depending on what you unchecked. You can either run the programs from the Start menu or you can run MSCONFIG again and add the programs back until youhave a balance between running applications and enough resources to smoothly operate your computer.

Also perform the steps given in the following email.

Deleting Temporary files:

Temporary files are normally deleted when the program is closed. Usually the temporary files are created in C:\Windows\Temp directory. It is recommended to delete these files on a regular basis by following these steps:

1. Double-click the My Computer icon on the Desktop.
2. Double-click the icon for the C: drive.
3. Double-click the Windows folder.
4. Double-click the Temp folder.
5. On the menu bar at the top of the screen, click Edit and then click Select All. All files in this folder should be highlighted.
6. Verify that you are in the C:\Windows\Temp folder.
7. Press the Delete key on the keyboard.
8. Answer Yes to any prompts about deleting files.

NOTE: If you receive a message stating that a particular file cannot be deleted, continue deleting the remaining files until as many files as possible have been deleted.

Hard disk maintenance:

ScanDisk and Disk Defragmenter are the two utilities that should be run on a regularbasis. ScanDisk checks for errors on the hard disk drive, while the Disk Defragmenter rearranges the data in contiguous clusters. Clicking Start, Programs, Accessories, and then System Tools accesses both of these utilities.

If you have a problem with either of these utilities not responding, run them in Safe Mode. To restart in Safe Mode, follow these steps:

1. Restart the computer.
2. Press F8 during Startup to access the Startup menu. Ignore any error messages that occur.
3. Choose Safe Mode from the Startup menu and press Enter.
4. Click Start, Programs, Accessories, and then System Tools.
5. Choose either ScanDisk or Disk Defragmenter.

I agree with previous answer!
Just few small corrections...
1. Prior to delete the tmp files, close ALL running programs.
2. The tmp files remaining, can be deleted manually from the DOS prompt (boot in DOS mode), type-->
cd..
cd \windows
cd \temp
del *.tmp

3. after deleting the temp files (with explorer and/or in DOS, REBOOT!

next, run defrag.

Do all this on a regular base, it keeps your PC run fast.