My laptop broke a few MONTHS ago and the hard drive had to be replaced, and I was told by the guy who did it that I needed to put in the CD that came with the laptop and then it would be fixed. However, I didn't get a CD with my laptop so I ordered one from HP.

When I put the CD in though, it just says "invalid system disk". I have had the disk replaced TWICE so I'm quite sure it's the right one, but I don't know what to do!

I would really appreciate some help!try formatting the disk BEFORE you use the CD...How do you know if the disk is formatted? And if it isn't, how do you format it?

Sorry if I'm just being stupid... Samaleyo, Don't beat yourself up as to a lack of knowledge.Until you have done it or studied it knowledge is not in the genes.Here is but one of many links the will give you the guidance.
http://www.mahalo.com/how-to-format-a-hard-drive
truenorth1. Boot from CD. It sounds like you need to tell the laptop to startup from the CD drive (HP Recovery CD) instead of the "empty" hard drive.

There's probably a function key to use during startup which will permit you to select CD drive as boot device (place HP Recovery CD in drive before making boot device selection). If not, you'd have to enter CMOS setup to change the boot device ORDER in BIOS (again via a function key or other designated key during system startup).

2. HP Support and Documentation. HP provides documentation and detailed instructions for many things. Your problem is one many users will face, and I'm sure HP has anticipated this and documented the appropriate steps (and function keys) you need to reinstall the operating system to your "new" hard drive.

My guess is HP will setup the new hard drive for you (partition and format) during the recovery process initiated by the HP Recovery CD. If I'm wrong we can deal with that later.

3. Model Number. Give us the complete Name and Model Number of the laptop, and I'll see if I can find the appropriate links on their web site for this information.thanks for the help!

Okay, I tried changing the boot order, but it STILL says "Invalid system disk. REPLACE the disk, and then press any key."

It's a HP Pavilion dv6599ea, I think that's the info you wanted?Are you sure you saved the boot order changes you made in bios, sometimes it can be confusing to 'exit & save changes' for beginners.
Equally as important is to have the recovery disk in the drive as well.The support page for your machine is: HP Pavilion dv6599ea Entertainment Notebook PC.

See subsection "Restore the PC to its original condition with the recovery discs" about halfway down within the following link: Using HP Backup and Recovery Manager

What operating system came with the laptop? Are the Recovery Discs for the same operating system?You may also want to remove the CD drive and re-seat it...there should be a release button right next to it.

The normal command to "save changes and Exit" from a BIOS setup menu is F10...The CD is for the correct operating system and I'm sure that I saved the boot order, but it doesn't seem to have changed anything.

My laptop doesn't respond to the CD the way the HP website says, it doesn't seem to recognise it at all.Just for the heck of it, do you have a cd you KNOW is bootable? If so, try booting to it and see what happens - OR - try booting to the new recovery disk on another computer.Have you removed the drive and re-seated it yet ? ?