If you can tell us a little more about your system that would be helpful.
OS, CPU, RAM, Hard drive size, what anti-virus, are you running anti-spyware?
What browser do you use? What kind of internet connection do you have?
You get the ipdiag.dll error when you boot, when do you get the second error message?
ipdiag is certainly not a standard startup program, it may
indicate the presence of spyware. Here are some standard security checks you can do:
Is your Anti-virus
program current and updated
? If not you can download a free anti-virus program here (US Link): AVG Free
When you have downloaded and installed it you need to go online to register it and update it. (It will probably prompt you to do this.)
Once you have installed AVG uninstall your old Anti-Virus software.
Do you have any anti-spyware
installed? If not download and update all
of the following:Reboot your computer in Safe Mode
and run the anti-virus scan and anti-spyware scans there.
If you are not sure how to boot in Safe Mode there is a tutorial here: Safe Mode
I do not recommend re-installing windows except as a last resort. There are many experienced members of BC who may be able to help you resolve the problem if you are patient.
Let us know what you find.