I explored Xda forum and got the way of flashing stock ROM as suggested but after doing flashing now my phone stuck at dell logo.
Phone Description: ROM version 318, build 12821 and had followed the below steps to flash ROM
1.download drivers from Dell Official Site - The Power To Do More | Dell
to recognize my phone to PC , while updating the dell streak usb driver in your PC
2. then download the recovery image of 318 from the following link http://forum.xda-developers.com/wiki/index.php?title=Dell_Streak
4. download update package 318 from same link.
5. download multirecovery flasher " http://www.4shared.com/file/p22LB2uD/MultiRecoveryFlasherv051.html" and unzip it in c:\ drive
6. rename the update package into update.pkg if its in other name
7. place that update.pkg into sd card and recovery.img into the multirecovery flasher folder and name that multirecovery flasher into some easy name like "streak".
8. then make sure that dell streak is recognized in your computer
9. then turn your dell streak off and wait for 5 sec and then press power button as well as camera button at the same time and it will show a white screen with fastboot option on the right top side
10. then wait untill there is a msg like, 'waiting for fastboot device'
11. wait for 10secs and then plug your usb cable of dell streak into your computer.
12. wait for fastboot mode_ txt.
13. then go to the command prompt in your computer (press start-accessories-command prompt)
14. then type ('"c:\.......) cd\ " )
15. then type (" c:\)cd streak ")
16. then type ("c:\streak)fastboot -i 0x413c flash recovery recovery.img ")
17. press enter, and wait untill success report pops up.
18. then type ("c:\streak)fastboot -i 0x413c reboot "") and remove the battery
19. dont let the phone reboot instantly press both volume up and down as well as the power button at once
20. then phone will turn on in recovery mode
21. select option "2. upgrade rom from update.pkg from sdcard option" with the help of volume down key and press camera button to start then
BUT AFTER THAT PHONE IS STUCK AT DELL LOGO NOTHING HAPPENING....