Nexus 7 boot stuck on Google logo

[shakthi...@gmail.com]

I followed all the instructions and was able to successfully build TaintDroid. I was also able to flash the images using the commands below. However, when I start to boot my tablet it stcuk on the Google Logo. If any on you can help me resolve this this issue that would be very much appreciated. Thank you!!

cd out/target/product/grouper  
fastboot flash system system.img 

fastboot flash userdata userdata.img