message: disks needs to be checked for consistency?

If it lets you in, find the icon for the disk (it should say C: among other things) and right-click that.  You want the tools so you can schedule a CHKDSK.  You can't run one directly because it needs exclusive access to the disk to be effective.

Run chkdsk!                             

It means it isn't sure whether there is a disk problem and you should check it. It may come to nothing.

Personally I too do this in DOS, by going to a DOS prompt as administrator, typing "chkdsk /f" (without the quotes, and pressing Enter. It'll then tell you it can't do this as the disk is in use and ask if you want it to happen on the next boot. Type Y and enter.

Then reboot and the check will happen. It will check the disk and attempt to fix any problems it comes across. It is very quick and there will probably be no issues. Then it will complete rebooting.  All done.

This indicates either an improper shutdown (not hardware issue, file system just needs to catch up) or the disk is failing, and bad sectors were marked.  You can run a dos prompt as administrator then chkdsk (enter) at the prompt (check disk).  When it finishes, if bad sectors are indicated, it could be a sign the disk is failing.

Just let it get checked. It's a maintenance routine that's best left undisturbed.