It may be that the BIOS does not recognize the new CPU and need an upgrade but with very little info on said motherboard I think you'll be frustrated with it.
That's the deal with proprietary systems, not very upgradable. I'd suggest that you save up some bucks and build yourself a clone system.
I've built a Celeron G540 system with 2x2 gig memory for under $200 but I used my old HDD and DVD-RW as well as my monitor, keyboard, mouse and Vista OS. This 2.5 Ghz Celeron is quite fast and run very well.
The new parts were CPU, motherboard, memory, PSU and case.