Why can't I use iTunes, and other computer problems?

I have two or three problems, and I don't think that they are related.

The first is that, whenever I open iTunes I get this error message:

"The application or DLL D:\Program Files\iTunes\MPlugin.dll is not a valid Windows image. Please check this against your installation diskette."

When I try to re-install iTunes, I get this message:

"The Windows Installer Service could not be accessed. This can occur if you are running Windows in safe mode, or if the Windows Installer is not correctly installed. Contact your support personnel for assistance"

I've tried all the steps found here: http://support.microsoft.com/kb/315346 to no avail.

Also, whenever I try to open a program from the Start Menu, nothing happens. However if I launch it from the Command Prompt, it will open.

The final problem is that I've hidden my desktop icons, but now I can't re-enable them.

I'm running Windows XP Professional on a Dell laptop. I have Avast! for an antivirus.

Thanks!

Why can't I use iTunes, and other computer problems?anti virus scan

An approach to solving your problem is by first checking your system integrity. This can be done having the XP installation CD, putting it in the CD tray and then running the System File Checker tool that comes with XP (which is commanded by "sfc /scannow" in "Start"%26gt;"Run"). If you can accomplish this step and let Windows verify your system is OK, then run Windows Update and let all the updates be downloaded and installed in your laptop. That could help at a glance, but it would be better if you post your results as soon as you try the former steps. Good luck.