black screen on login (cant start lightdm)

[hasanaa]

installed elementary alongside win7 on uefi system. everytings went fine. after upgrade & reboot, i select the os in GRUB, it takes me to a black screen. tried “service lightdm start” and “startx”, didnt work. what should i do?

[hasanaa]

~$ lspci | egrep "VGA|3D|Display"
00:02.0 Display controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
01:00.0 VGA compatible controller: NVIDIA Corporation GT200 [GeForce GTX 260] (rev a1)

~$ glxinfo | grep render
direct rendering: Yes
GLX_MESA_multithread_makecurrent, GLX_MESA_query_renderer,
OpenGL renderer string: Gallium 0.4 on NVA0
GL_MESA_texture_signed_rgba, GL_NV_conditional_render, GL_NV_depth_clamp,
GL_NV_blend_square, GL_NV_conditional_render, GL_NV_depth_clamp,