PCLinuxOS 2010 uses Grub Legacy (a.k.a. Grub1) by default. Sabayon Linux 5.2 uses Grub2 by default. Grub Legacy and Grub2 are effectively two different bootloader products and are incompatible, although each can be configured to chainload the other. Furthermore, Grub2 is beta release software and still flaky. Nevertheless Grub2 is 'the future' and various Linux distributions (including Ubuntu) have already adopted it as the default bootloader. Grub2 still has limitations and no doubt some bugs, and using it becomes even more complicated when mixing it on multiple-boot PCs with distributions that use Grub Legacy.
I'm going to suggest three alternative ways to try to resolve your current problem:1. Use the Windows bootloader to chainload Grub Legacy for PCLinuxOS and Grub2 for Sabayon Linux
To do this you would need to perform the following two main steps:
1a. Restore the MBR on the internal drive to the Windows Vista/7 MBR code
You can do this either by using a Windows Vista/7 installation disk or a Windows Vista/7 System Recovery Disk that you made when you first bought the PC. If you don't have a Windows Vista/7 installation disk and you didn't make a Windows 7/Vista System Recovery Disk then you can download the latter from various Web sites (Download Windows 7 System Recovery Discs
is one such site in the case of Windows 7).
You can then boot the Windows installation/recovery disk, launch Windows Recovery Environment and run Bootrec.exe to restore the MBR (see How to use the Bootrec.exe tool in the Windows Recovery Environment to troubleshoot and repair startup issues in Windows
for instructions). That way you should be able to boot at least Windows Vista/7.
1b. Configure the Windows Vista/7 bootloader to chainload Grub Legacy for PCLinuxOS and Grub2 for Sabayon Linux
Boot into Windows Vista/7 now that the MBR has been repaired, download EasyBCD 2.0 Beta from the NeoSmart Technologies Web site, install it and then use it as per the instructions on the NeoSmart Web site to configure the Windows Vista/7 bootloader to chainload Grub Legacy in the PCLinuxOS boot partition and Grub2 in the Sabayon Linux boot partition.2. Configure the Windows Vista/7 bootloader to chainload Grub Legacy for PCLinuxOS, and configure Grub Legacy to chainload Grub2 for Sabayon Linux
If you have trouble configuring EasyBCD to include both a Grub Legacy distribution and a Grub2 distribution in the Windows bootloader menu, then an alternative would be to configure the Windows bootloader to chainload Grub Legacy in the PCLinuxOS boot partition and then configure Grub Legacy to chainload Grub2 in the Sabayon Linux boot partition. To do that see the instructions Chainloading to GRUB2
in the Gentoo Wiki article on Grub2.3. Restore Grub Legacy to the MBR and use it to chainload Windows and Sabayon Linux
If you are not prepared to use the Windows bootloader and configure it using EasyBCD then you could: a) restore Grub Legacy to the MBR either by using Super Grub Disk or by booting the PCLinuxOS LiveDVD, chrooting into the PCLinuxOS HDD installation and using Grub Legacy commands (see Gentoo Linux Handbook - 10. Configuring the Bootloader
* or No OS boot selector [Solved]
); b) configure Grub Legacy's grub.conf in the PCLinuxOS boot partition to chainload Sabayon Linux (see the above-mentioned Gentoo Wiki Grub2 article) and to chainload Windows (I expect grub.conf is still configured as such on the PCLinuxOS boot partition).
* Note that the Gentoo Linux Handbook is currently written for Grub Legacy.
Note that partition numbering starts at zero in Grub Legacy but starts at one in Grub2. Disk numbering starts at zero in both Grub Legacy and Grub2. Thus /dev/sda1 would be (hd0,0) in Grub Legacy but (hd0,1) in Grub2.
By the way, posting a request here to the SL developers may well not be read by the applicable person. I suggest you either create a thread in the appropriate shed (forum), which is 'Artwork and Development Suggestions', or file a bug report detailing what happened (see link 'Bugs' at the top right of this page).