Beaglebone Black not booting due to modification of uEnv.txt

I accidently modified uEnv.txt file located in eMMC of my Beaglebone black. Now the board is not booting. I can not even see BBB for serial connection from terra term ( I installed all the drivers for Win 7). How can I get access to the board? If I can just access to uboot I could reflash or run it using nfs. Any ideas?