Macbook pro with OS X 10.6.4 will not update to 10.6.8
I bought my macbook pro in 2010 with Snow Leopard 10.6.4. Over the years I've kept up with the Snow Leopard updates, so I've been using 10.6.8. Recently I decided to upgrade to Mavericks, but first wanted to reformat my hard drive to wipe off a lot of junk that's accumulated. I reformatted it with the disks I got when I bought my mac, meaning the operating system I reinstalled was 10.6.4. I knew I needed 10.6.8 or later in order to upgrade to Mavericks, so I ran the software update to bring everything up to speed.
The problem I'm having is my mac just won't update to 10.6.8. I tried it several times through software update. When that didn't work I tried downloading the 10.6.8 update combo directly from Apple's website. I can download it, but everytime I run the file it gets up to the point where it starts installing, then says "installation failed". Of course, now I can't upgrade to Mavericks either because I'm stuck at 10.6.4.
If anyone has any suggestions or advice as to what might be wrong I'd really appreciate it, I can't figure it out.
MacBook Pro, Mac OS X (10.6.8)