The LGA 775 processor socket doesn't matter, calderwooddu.
It's up to the motherboard chipset, and the BIOS program, and version, of what that Foxconn N15235 will support. I would go back to the Pentium Dual Core E2160, use CPU-Z from CPUID.com, (Free), and see what the motherboard chipset is, first.
(Motherboard chipset: The Northbridge, and Southbridge chips. Chip is slang for I.C. Integrated Circuit)
The Northbridge chip is what determines what Processors are supported.
Since the E2160 is built upon the 65nm technology, and the E5400 is built upon the 45nm technology, the Northbridge chip of the Foxconn N15235 may not support the E5400.
With the technology change are also Instruction Set changes. Plus other parameter changes. The BIOS program, and version on the Foxconn N15235 may not support these, either. Sorry to be a bummer.
Not a solution per se, Yet.
Need to know what computer this Foxconn mobo is out of. (MOtherBOard)
OR, if you get the computer operational again, let's use CPU-Z to see what the motherboard chipset is.
Need help in downloading, and/or installing CPU-Z, post in a Comment.