Cant install Win 7 showing CD/DVD drive error

i cant install windows 7.
whenever i try - it says "a required CD/DVD drive is missing " something like that ....

i don't know what to do.....

before this i tried to install XP but it was also a fail .... i reached upto partitioning my hard disk and hit install XP ...but after reboot it show disk read error ....
and i tried win 7

mine is a core i5 , GYGABYTE GA-PA65-UD3-B3 motherboard
4 gb RAM, 500gb hard disk.
my CD ROM - SONY DVD/CD RW - model no. DRU-880S

please help..... i have been trying this for a week

This error is typically a bad ISO or burn.

Where did you get Win7? Is this a DVD your burned yourself? If so, confirm ISO integrity and burn another using ImgBurn at 4x speed with Verify.

Try USB flash stick install as suggested. This tool is easiest, with Win7 in dropdown menu: Universal USB Installer – Easy as 1 2 3

Check the hard drive with the manufacturer's diagnostic tools.
Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.
HD Diagnostic

this is all what happened ....
i tried to install XP, so i put the XP CD, it started, i agreed the policy, then deleted all partitions except the 'system reserve' disk 'C' which was like 100 mb.... so i deleted all other partitions and divided into three new one .... and installed in one among them ..... so it started formatting in NTFS .... next, as you all know, started showing the formatting status ..... and it was done ..... and started automatic rebooting to install XP...but after the reboot it never installed XP instead it shows 'disk error' .... then i changed my bios boot menu like ....1st CD rom ...2nd HDD ....3rd USB ...likewise .... but it was no help..... and i started installing 7 .... now the thing here is that .... i tried the CD installation process ..'en it will go up to 'install now' step ....and i hit the 'install now' button and the dialogue that i mentioned earlier popped up....and as my friends here suggested to use bootable USB ...i've tried to make one ....i have a tool ...there is no specific name for this software...it just says windows 7 usb-dvd tool ...this was the program that i downloaded via utorrent from H33T. i have a 8GB GENX USB .... and i cant make it bootable through this software....it says that i don't have enough memory ...but i just formatted my USB ...and its completely empty .... i dont have access ....it wont boot ...even xpressrecovery was helpless ....

I gave you the steps to burn a confirmed ISO to DVD or write to flash stick, which you apparently ignored.

How do you plan to activate Win7?

thanks guys ....thanks Mr gregrocker the USB tool you suggested works perfectly and my PC is back on .....i hope i could count on you guys if i have any problem with my PC in future ...... thanks again ....