how to make a bootable USB with Oem windows7 (no disks)

Dell - Creating Your System Recovery Discs with Dell DataSafe Local Backup 2.0:

http://support.dell.com/support/topics/global.aspx/support/kcs/document?docid=DSN_62A668E1C399857AE040AE0AB8E12942&isLegacy=true

HP - Create a set of operating system recovery discs:

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c01895783#WhenCreate

Toshiba - Creating recovery media using Toshiba Recovery Media Creator:

https://www.csd.toshiba.com/cgi-bin/tais/support/jsp/bulletinDetail.jsp?soid=2753749&pf=true

Gateway - Using System recovery:

http://support.gateway.com/s/SOFTWARE/Medialess/FAQ/SUPPAGE01su44.shtml

You can make a USB repair drive:

How To Repair Windows 7 From USB Flash Drive:
http://www.intowindows.com/how-to-repair-windows-7-from-usb-flash-drive-repair-without-installation-dvd-disc/

Create A System Image In Windows 7

After you install and activate Windows 7 create a system image as a backup for your current computer in case you ever need to reinstall it. This will restore your computer to it's exact state when the image was made - that will save you the trouble of having to reinstall Windows 7 and everything currently installed again, and it takes much less time to do.

1.  Click the Start Menu and type "Back Up" then click on Back up your Files.  

2.  In the Control Panel window that appears, Click the blue Create a system image link.

3.  The Create a system image window should pop-up.  Select which hard disk, DVD, or network location you are going to save your system image to.  Click Next to continue.

4.  On the next page check both your System and System Reserved drives.  Once you have selected the drives Click Next to continue. Note: You can select as many drives as you want (if available), but the more you choose to include means the larger the image size will be.

5.  The next window is just a review, make sure everything is correct then Click Start backup to start the process.  This can take 10 minutes or more so patience is required.

6.  After the backup completes, you?ll be prompted with the option to create a system repair disc.  This is a good idea just in case your system has any problems in the future.  Click Yes.

7.  Choose which Disc Recording drive you?ll be using to burn the disc.  Insert a blank CD or DVD to the physical drive and then Click Create disc.

How To Restore Windows 7 from a System Image

http://www.howtogeek.com/howto/7702/restoring-windows-7-from-an-image-backup

You can also use a free hard drive imaging program - the two below will have more features then Windows 7 built in imaging program. Both enable you to make a boot disk to start the recovery, and both programs allow you to divide the backup to multiple DVDs. If imaging to a different hard drive these will work better.

Reflect Disk Imaging (free):

http://www.macrium.com/reflectfree.asp

Paragon Backup & Recovery Free Edition:

http://www.paragon-software.com/home/db-express/download.html