Task Manager not opening

Right click the task bar at the bottom of the screen, and select task manager.
Doe it work that way?

Ouch.
That's part of a nasty rootkit which disables your task manager.

90% confident you have got some nasty malware/virus.

I could talk you through how to get rid of it but there are better things written and I don't know what you have.

This is a symptom of a anti-virus spoof malware where it'll come up with security essentials or something saying it found stuff and ask you to remediate.

If you're not very experienced with computers then you may want to backup your data and use the system restore discs.

You may try going into safe mode and using system restore(if it'll let you), some of these will disable/corrupt safe mode however.

Goodluck!!!