HP pc sometimes boots to black screen w/cursor, somtimes to OS

[rrjljrw]

This is a HP Pavilion, 80gb hdd, 2.2 ghz (I don't recall the rest of the specs) about 2 years old. It was brought to me with the problem of sometimes booting to a black screen with a blinking cursor, sometimes into the OS (win XP home). When it would boot all the way, it was extremely slow. I tested the hdd, and it errored out on the long test. Replaced it with whatever Samsung felt like sending me (don't know if it's refurbed) and used HP recovery cd's to reinstall. The hdd tested fine. Now it's doing it again. I ran all the updates from Microsoft, and updated the bios. Weird thing I noticed is that the boot order has to be setup so the top of the list is what you want to boot to. When I had to boot to fdd, I had to set this up first in the order. None of the other components would power when going through the bios, but the hdd is always detected. In order to boot to hdd consistantly, I had to set that first in boot order. I'm wondering if perhaps a cd drive is going bad. Any ideas? By the way, HP seems to have a new way to update the bios, and it doesn't involve flashing it. It was just software that was installed.