Maybe some malware, or you installed some programms and blindly clicked "Next" without looking at what was going on.
Many programms offers you to set your home page to this or that page, on by default.
Many programms also offers you to install mostly unneeded tool bars everywhere, also checked by default.
They expect you to blindly click through the installation process.
If you blindly click through the install process, you explicitely agree to the changes and installations.
It's possible that you can use a restore point to undo some of the installation responsible for those changes.
You may not be able to undo all the changes if they are to numerous or to old.
Navigate to your usual home page end set it as your home page.
In MS Internet Explorer, right click the bars, in the menu that comes up, uncheck any unwanted tool bar.
Go in the "add and remove programms" and uninstall unwanted programm.
Install some antivirus like the excellent AVG, available for FREE at free.avg.com and to a full scan with automatic eradication turned ON (default setting).
Next, download and install Spybot Search & Destroy (also free). Do a scan and remove any nasties found.
Activate it's homepage hijacking prevention option.
When installing ANYTHING!
ALWAYS take the time to eveluate what is proposed.
UNckeck any change or optional installation you don't want, like tool bars.
Refusing those will not affect your ability to use the programm.
Unstalling the programm that had those addons coinstalled usualy DON'T remove the bars.