I have recently bought a second-hand 500gb SeaGate HDD. I already had a 80gb SeaGate HDD installed in my SATA 1 slot. I have tried plugging in my second hard drive to the only other slot (SATA 2 slot). When I boot my computer, both hard drives appear as they should. However, they don't appear in Disk Management at all. Please help I don't know what is wrong and desperately need this larger hard drive.
Also if it is easier I could transfer all the content from my existing HDD to the new and just have the 500gb HDD installed. However, I can't find a way of transferring everything (including my OS) for free. If you know how to do this please advise.
You say, " both hard drives appear as they should. However, they don't appear in Disk Management at all." First, I'm not sure what you mean by "They appear as they should". Where? Have you gone into BIOS Setup to see them, or are you just seeing quick notes about them in the POST start-up screens? In either case, if both are acknowledged as present, then they are valid hardware devices and Disk Management REALLY should see them.
So, check again in Disk Management. Look particularly at the LOWER RIGHT pane where all devices are shown. NOTE that this pane SCROLLS so you can see them all. Check for each HDD and optical drive in your system. You should find both HDD's there. Now, the older 80GB unit should be bootable and in use as your C: drive. The newer 500 GB one may only show as one large block of Unallocated Space. In that case4 you have two choices.
1. IF you want to continue using the 80 GB as your C: drive and just add the 500 GB for data storage, then you can RIGHT-click on the Unallocated Space and choose to Create a new Partition in it, then Format it. Some versions actually combine these two steps into one called Initializing. Either way, this should be a Primary Partition that does NOT need to be bootable, and I expect you want it to use up ALL of the available space. For the Format options, set it to use the NTFS File System and let it do a Full Format, which will take HOURS to check the unit thoroughly. When done, back out of Disk Management and reboot to update the Windows Registry.
2. IF, instead, you want to have the large 500 GB unit take over as your boot drive and become C:, you need to clone the old smaller drive to it. For that you need free software, and rgd1101 recommended Clonezilla. I have not used that, but I have used the free package from Seagate for their drives, called Disk Wizard - it appears to be a customized version of Acronis True Image. Either can copy absolutely EVERYTHING from the old 80 GB to the new 500 GB unit, putting everything where it belongs. You do NOT need to Partition or Initialize the 500 GB unit first - that is all done by the cloning tool. I will alert you to one "problem" I've had with cloners before. In your situation by default it will try in its first step to create on the 500 GB unit a new Partition that is the SAME SIZE as the old 80 GB unit to receive the data. This is NOT what you want, I'd bet. I expect you would want ALL of the 500 GB unit in one drive called C:. So, when it offers you a group of settings and asks you to approve and proceed, do NOT approve. Instead, use the menus to change the parameters so the new Partition is the full size of the HDD (probably about 465 GB), with other parameters as above (except, of course, this Partition WILL be bootable because it is to become your C: drive). When you have it set as you wish, proceed and wait patiently.
If you do clone to the larger drive, here's my next suggestion. When done, shut down and unplug. Disconnect the data cable to the 500 GB unit. Now take the data cable at the older 80 GB unit and leave its mobo end plugged in, but take the HDD end and move it to the new 500 GB unit. unplug the power cable at the 80 GB unit. (You can leave the 80 GB unit in the case, or remove it for now.) When you boot up, the machine will boot from the SAME SATA port of the mobo that it always did, but this time your C: drive will be MUCH bigger. The disconnected 80 GB unit is now a perfect backup of everything up to this point. Keep it unused for a while until you're SURE that the new setup is working just fine. Then you can decide how to re-allocate the 80 GB unit to some use - maybe just a second HDD for data.