1.  No.  You ordered them without an OS.2.  No.  Must be purchased with the system. You have two options: 1.  Return them, then repurchase with an OS.2.  Purchase a Retail Windows license for each machine. You may be able to work out a deal with a local system builder to sell/repurchase with OEM license (generic/Microsoft OEM which is a lot cheaper than full Retail), but the system builder's cost on deal like that would probably make it the same as going with Retail in the first place.  You can't purchase generic/Microsoft OEM software for your own machines. 
I have  ordered  30 laptop without os. There are  received me. But now I have to install OEM os with a dell COA sticker. 1.Can I do this??? 2. Can I order above oem os with a dell coa sticker for my purchased machine separately  from dell?  Thanks....
OEM license key of dell for windows 7 professional 64 bit 