For best results follow my wiki A Clean Install of Windows 7.
Some viruses can survive a format with the Windows 7 DVD. To completely wipe it is best to use DBAN (Step 7a) and then to reinstall Windows 7. The wiki explains the steps in great detail.
The wiki takes you through the install step by step.
Elaborating on the DBAN this is an additional step which will securely wipe any data on your hard drive. It will remove all viruses. Note it will take a few hours as it securely wipes it.
Before using DBAN any card readers need to be disabled in the BIOs setup. DBAN stalls if a card reader is present but has no card in it. To access the BIOs setup power down your system and then power it back up. At the Dell BIOs screen press F2.
In the BIOS setup there should be a category called onboard devices, expand it. Within this category you will be able to disable the card reader. The BIOs setup should look something like the following, there are variations depending on the model:
Note: The mouse/touchpad isn't present in the BIOs setup, you will have to use the keyboard arrow keys to move between the fields and enter to select a setting. When finished, press esc and you will be prompted to save and exit or just exit. Select save and exit.
This is only necessary for systems with card readers. Be careful when changing any BIOs settings. I don't recommend changing any other setting unless you know what you are doing. If you change a setting I recommend taking a note of it just in case.
Insert the DBAN CD/DVD or USB and power down your system. Press F12 at the Dell BIOs screen and select boot from CD/DVD or from USB respectively.
Follow the onscreen instructions to completely eradicate any data on your hard drive.
Note DBAN may take some time as it does a full format of any data on the hard drive.
Once the DBAN format is done, re-enable any card reader within the BIOs setup.
You then proceed with the installation of Windows. Please provide the model of Dell for additional help. Also do you have your Windows 7 Reinstallation DVD? Does it mention f its 32 or 64 bit and does it mention Service Pack 1?
Maybe natakuc4 knows something I don't but if you format (long) and reinstall os I always assumed any nasties would be wiped out.
LAZ123 The Windows Format is quite light (which is why it is quite fast). In fact I think the Windows Vista/7 format are even lighter than the Windows XP one as they take a much shorter time to format.
We have had people on the forums who have still have retained an infection after using the Windows DVD to format and then reinstall the operating system. They have had not kept the infection after a format using a DBAN DVD and then reinstalling the operating system.
Some Malware/Viruses will be wiped out by the Windows format but not all. DBAN will get rid of everything which is why I recommend use of DBAN. See this post here for example.
I don't understand your steps 2-6. What step should I start if I just want to reinstall Windows 7? why would I download service packs and drivers in the first steps then reinstall windows 7 , if I will download them again in the last steps?
I don't have the Windows 7 reinstallation DVD, but I have Drivers and utilities DVD.
The idea of step 1-6 is to prepare for the installation. Step 1 ensures you have all your data backed up. Step 2 mentions Belarc Advisor as it often obtains product keys e.g. for Microsoft Office. Step 3 is getting the Windows 7 DVD (explained later).
Step 4 and 5 are downloading the service packs and drivers required and copying them to a USB stick. Usually one can't access the internet when a system only has Windows on it because the drivers aren't installed. This is why I mention downloading all you need and saving to a USB stick/external hard drive before starting the Windows. You don't bother installing them at this step. You insert the USB in your computer after Windows is installed and then install the drivers.
Step 6 is preparing SATA drivers this is sometimes required so Windows 7 can find the hard drive e.g. for newer advanced format hard drives.
Step 7a is optional, it will format the computer more thoroughly than the Windows DVD, its geneally not recommended but if you really want to delete all personal data and/or get rid of a virus its recommended.
Step 7b doesn't apply to your model.
With regards to the Windows 7 DVD, you will have to request a Dell Reinstallation DVD or use a retail .iso and phone activation. This is covered in Step 3.
Dell are currently shipping out most of their systems without reinstallation DVDs. For US customers there is an online request form for Reinstallation Media. For those customers not in the US you will need to contact Dell technical support and ask for one. The customer numbers are available here. This is the most recommended route.
Alternatively Windows 7 retail .iso files (supplied by Digital River) may be found in my Microsoft Windows and Microsoft Office Downloads wiki. Ensure that you can read your 25 digit product key on your Windows COA before attempting installation with a retail .iso. This COA may be found on the base of your laptop or sometimes under the battery.
Step 8 begins the actual Windows 7 installation.