Here is a redhat bugzilla entry about this problem:

https://bugzilla.redhat.com/show_bug.cgi?id=239931


Roelof van der Kleij wrote:
> Some 64 bit kernel / bios combinations have problems with >= 4 Gb of
> memory. If you have that, try it with only 2 Gb of memory installed. If
> this is your problem, try playing with memory mapping bios settings.  In
> my case, I ran into it with an Intel DQ965GFE motherboard after a bios
> upgrade.
>
> Roelof
>
> Maccy wrote:
>> I'm having some problems trying to get SL4.5 to run properly on an 
>> Intel Core 2 Duo system with Intel DQ965GF mobo and 2 x SATA II 
>> disks. The O/S installs fine but takes forever to boot up and run.
>>
>> I've tried adding a number of kernel parameters including 
>> all-generic-ide, irqpoll, pci=nommconf, acpi-off and 
>> selinux_compat_net=1. The Intel Quick Start Kit available for that 
>> board reports that all necessary drivers are already installed. The 
>> BIOS drive configuration is set to ATA/IDE=Native and SATA=AHCI. I've 
>> experimented with other BIOS drive settings to no effect, and also 
>> built a newer kernel (2.6.21) from source.
>>
>> Of course Scientific Linux 5.0 installs and runs without issue but as 
>> all our other machines are 4.5 I'd like to get it going on this!
>>
>> Any advice appreciated,
>>
>> Mark