could possibly be an infection
Have you tried to start the computer in safe mode? safe mode with networking?
you are advised to look on the manufacturers website, to see if you can download the full manual for the computer.
The manual contains the instructions for starting safe mode, possible recovery / system restore mode options. These instructions are different, NOT the same for all computers. You may need to look in the manual for your model.
Have you tried to update, scan computer, with your
existing antivirus?
do you have the microsoft windows 7 basic installation disk?
put the disk in the drive and start the computer
if the disk will run, select: "upgrade"
this repairs the operating system in many cases.
this does not erase your personal files, but sets the
operating system back to a default state. hopefully
it runs again like normal.
I cannot say that it will work %100 of the time, but
if the computer is infected it might not work...
OR have a computer shop do any of the above for you.
Making a backup of all your personal files and pictures
(etc) is very important. After the computer is able to start
up again, make backups in case of future problems.