As the Dell BIOS does probably not permit to create a working mp-table, it is maybe worth to try to boot with the kernel parameter:
Code:
pirq=x,y,z, ...
(where x, y, z, ... are the correct IRQ entries for the Inspiron 5150 board.)
This is the only thing I've not tried yet (and I will never try,) since it requires a lenghty try-and-error process to find the correct IRQ entries.
Anyway it seems to me the only thing left to try.

For more info on the subject, consult the document IO-APIC.txt shipped with a stock kernel source tree and/or the linux-smp mailing list archives.

Bye,
Emanuele Zeppieri.