Ubuntu 64 Bit not working acer p253e

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http://askubuntu.com – I have read the others about this but to no avail. I installed Ubuntu 12.04.2 64 bit and then did an update but now Ubuntu won't boot. I have checked to see whether my Laptop is 64 bit (dual core) and it is. 12.04.2 worked tho. 12.10 64 bit not. It comes up on the splash and then goes black and I can't do anything. I want to develop for Ubuntu Phone (porting) so need 64bit. Also 32 bit works even with 13.04. Is this a known problem with 64 bit after 12.04 and how can I boot into safe mode? Can't even edit boot options. The Specs are: Resolution 1366 x 768, 16:9 Format Intel® Pentium B960 (HowTos)