You need to reinstall the system using the licence number on the sticker usually placed at the bottom side of the laptop.
Microsoft does not distribute replacement disk to reinstall OEM licenced Windows, so that you will need to find a disk.
If you want to purchase a new licence, you can get one from the Dell store.
A common way to proceed is downloading a disk with the operative system corresponding to the version on the sticker (eg. Windows XP Home), and reinstalling the system.
This practice is not endorsed by Microsoft, but it is not illegal, providing that you use a genuine licence number valid for installation on this computer.
THis is the operation performed also at local computer shops to reinstal OEM operative system.
The operation is done for a small fee at computer shops. A good option would also be having the job done at a local shop.
If you want to DIY, you will need a Windows install disk of the same version printed on the licence sticker.
A way to get the disk is by downloading the disk. Please be aware that most persons making the download available are breaking the law by also providing invalid licence numbers or programs to disable Windows Validation procedure. If you decide to download the disk, also be aware that software distributed in this way may contain viruses.
In no case use a licence that does not belong to your computer genuine license, or does not come from a genuine Microsoft system COA sticker that can be installed on your computer.
To download the disk you will need at least three programs:
1) a p2p downloader: µTorrent
2) a p2p search utility: Convivea - Bit Che
2) a CD/DVD burning utility: Free CD/DVD burning
Install the downloader, then the search utility. Search a Windows disk for your same version. Choose one that does not offer crack or validation cheating. Download may take over one day to complete.
When download is complete burn a CD by installing CD burning software.
Start the C610 with the Windows disk inside and reinstall Windows.
After installing the operative system you will need to download and install all the software drivers listed here.
The operation is quite complicate, and system reinstall is suggested to an advanced computer user.
If you have not done anything similar before, better taking the laptop to a shop, or contacting Dell to arrange a repair. This will also exclude the risks related to download of not verified ( and often non-legal) software using P2P.
Repair cost at t shop starts at about $50.