Hardware upgrade and boot issues

[PleegWat]

Hi all,

Today I upgraded my system from a several-years-old pentium D to a 
brand-new core i5. I've preserved my existing hard drives, although I 
did make a backup.

After quite some fiddling, I managed to get it to boot up. I replaced 
the standard 32 bit kernel by the pae version, and it took another 
several attempts to get the system to boot.

I've got the splash screen disabled; when the system stopped booting the 
last couple of lines were either about usb initialization or about 
invoking fsck.

What could be causing these issues? Are there any packages I should 
reconfigure or bios settings I should check?

Also, is there any hope of upgrading to 64-bit while saving me the 
hassle of reconfiguring my installation from scratch, or should I just 
do a clean installation anyway to get stuff stable again?

Thanks in advance,

PleegWat