|If you don't shut down Windows properly, CHKDSK will want to run the next time you boot the computer - that's normal - let it run.|
How long it takes to run depends on how much ram you have, the speed at which your computer runs, and how large the partition, or partitions, is/are it is checking.
You have not supplied any info about your system.
What brand and model of brand name system do you have, or if it's a generic system, what's the make and model of your mboard?
How much ram do you have?
What's the speed of your cpu?
How much data is on your C drive?
However, it should NOT literally take hours, unless there's something seriously wrong.
If you did Shut Down Windows properly, or if the computer restarted without you knowing what caused that, and/or if CHKDSK wants to run frequently while booting and you can't think of any reason for that, that's not normal.
We need more info from you.
Do you have other symptoms? If so, tell us what they are.
Have you been fiddling with components or connections inside the computer case since the last time the computer worked correctly?
Have you changed which ram you have installed since the computer last worked properly?
If you HAVE NOT,
Check your hard drive with the manufacturer's diagnostics.
See the latter part of response 1 in this:
(thanks to Dan Penny for this link:)
Hard Drive Diagnostics Tools and Utilities
If you don't have a floppy drive, you can get a CD image diagnostic utility from most hard drive manufacturer's web sites, but obviously you would need to make a burned CD, preferably a CD-R for best compatibilty, on another computer if you need to.
If the hard drive itself tests okay, any data problems found can be fixed, one way or another.