This is likely a difficult issue to deal with. The NVIDIA 600 series chipsets are about six years old, which is very old in PC years. There are several possibilities regarding the cause of the issue, that all involve the 650 chipset, which is the main problem. The 650i chipset may not be able to negotiate the SATA interface speed with the 520, due to a protocol issue for example, so it sets it to SATA I speed. The NVIDIA driver (I assume) is able to do that with the HDD, but perhaps the latest protocols are not understood. While you say you don't have AHCI as a SATA mode in the BIOS, being able to select "Command queuing" is a part of the AHCI spec, but whether or not you are getting full AHCI functionality, I don't know. Are there any other options beside the "DMA Mode" available?
If you have Windows 7, you could try to load its native AHCI driver, msahci, which is a generic driver that works with many chipsets. But not being able to set the SATA mode to AHCI is a problem. In that same dialog box you posted for the properties of the NVIDIA controller, clicking the Driver tab and attempting to update the driver manually to msahci is the only method, if it even offers you msahci as a choice. What OS are you using? Have you ever used another SSD with your board?
The NVIDIA chipsets tend to have issues with SSDs, and usually that is their SATA operating speed. All in one PC manufactures like Dell tend to be much less flexible in their BIOS options, are you using the latest BIOS update for your PC? Does their website's forum offer any help with this?
"Have you ever used another SSD with your board?" No this is my first SSD drive.
"What OS are you using?" I'm using windows 7 professional 64bit
"Are you using the latest BIOS update for your PC?" Yes I have got the latest BIOS update 1.0.13 DELL released.
BIOS has no option other thank AUTO detect drive and RAID Config.
Below I have uploaded a photo of the compatible hardware the NVIDIA nForce SATA controller offers and I have got the latest update for nForce. I'm not quite sure how to update the driver to msahci, I looked through Microsoft controller drivers but I wasnt sure on which is it is.
It does look like that because the nForce controller isn't identifying the speed of the drive it has defaulted it to SATA1.
Ok, you've done everything correctly to attempt updating the chipset driver, that is, chose "Browse my computer...", but alas, msahci was not listed. If Windows thought it was compatible, it would have been listed. I fooled around with un-checking the "Show compatible hardware" that appears on the screen in your screenshot, and chose NVIDIA. It listed two drivers that Windows 7 has for NVIDIA chipsets, "nForce3 250 Serial ATA controller" is one, the other a PATA driver, which you don't wan't. I assume you don't see those since you have other NVIDIA drivers installed, or the ones I saw are not compatible with your chipset. I have no experience with NVIDIA SATA chipsets, so I can't predict what the result would be if you load it, if you even could. For example, it might help with the recognition of your 520 as supporting SATA II speeds, but might not give you AHCI/RAID features, such as command queuing, that was shown in your first post (really Native Command Queuing, or NCQ... I hope it referred to that!) which is the main feature of an AHCI/RAID driver that you want for best performance from a SSD. You'd need to uninstall the NVIDIA drivers you've loaded before the others I found might be displayed. But again, I really don't know if they would work better for you, if they would work at all.
A potential alternative for you would be getting a separate SATA II or SATA III interface card, that is used in a PCI-E slot on a mother board. Note I said PCI-E, not PCI slot, they are different. Does your board have a PCI-E slot? Any type/size will do, as in a second video card slot (not AGP!) that you don't use. The problem with these cards is, some mother boards won't let you set drives connected to them as boot/OS drives. Given your Dell board, it probably wouldn't, unless you could find an add-on card that guarantees it. Cards like this (SATA II, and cheap "SATA III" cards that are not really fully SATA III speed wise) can be had for $50 or less.
I know you were hoping to breath new life into an older PC by adding a SSD, which is a good idea that does work, but the NVIDIA chipset (which they no longer make) ruined it for you, along with the restricted BIOS of all in one PCs like a Dell, sorry to say. I hope someone with a NVIDIA chipset board can give you some better advice. Also, if in the military store/PX (I may have no clue what I'm talking about here) or in your travels (if you're out of the US), you have the chance to get a new board, etc, for a new PC at a good price, I'd go for it.
Regardless, if you're a veteran of Iraq or still serving there or elsewhere, Thank You for your service!
A little late, but here you go. This is what worked for me for my 320 120gb SSD. I have a 750i SLI FTW board for reference. You still won't have AHCI but you should see a little bit better performance with these drivers. And now the SSD toolbox will work
In Windows 7 -right click My Computer>click on Manage>Device Manager >expand Storage Controllers >right click NVIDIA nForce Serial ATA Controller >select Properties >click Driver tab >select update driver... >select Browse my computer for driver software >select Let me pick from a list of device drivers on my computer >select Standard Dual Channel PCI IDE Controller >select Next.restart your PC and the toolbox should work