upgraded to win 7 - now unusably slow and lagging

I'm a noob with this so please understand some ignorance on my end. Thanks in advance for any help!

I recently upgraded my Windows Vista home premium (64 bit) to Windows 7 home premium (64bit). Now everything takes forever to load (run) if it even loads at all. The CPU itself is only running at 15% when I can get task manager to load but the memory usage is at 66% (3 gigs).

I'm currently running a Gateway FX6800-01
Core i7-920
3GB of DDR3
Radeon HD 4850
Creative’s X-Fi XtremeGamer sound

I'm not sure what to do... BTW Safe Mode works fine.. aside from not being able to update anything properly.

Did you do upgrade or a clean install. (clean install is best)

Thanks for the replies!
Walker - I can't even run the 'WEI', it just freezes. I did run the windows 7 upgrade advisor prior to install and it said I was good to go.

Theog - I upgraded from vista... Sounds like I need to do a clean install?

I have 2GB of DDR2 RAM on 64-bit Windows 7 Home Premium and it runs perfectly with no lags or performance issues at all. I'm not saying that WalkerA WinTeam is wrong, I'm just saying that it's a possibility that the ram isn't the issue. Did you do an upgrade or clean install? If you did an upgrade, try reformatting your hard drive (backup first) and doing a clean install if you can, you can use an upgrade disc to do a clean install. What antivirus software are you running and is it up-to-date? Is Windows up-to-date? It's important to keep your system up-to-date with updates and drivers. Some antivirus software such as Norton and McAfee can slow down your PC, I highly recommend Microsoft Security Essentials with Malwarebytes and Superantispyware which are all free and don't affect your PC's performance. And don't forget to do a regular tune-up every once and a while such as cleaning your junk files and registry with something like CCleaner, and defragging your HDD with something like Defraggler. If you're willing to spend money (which isn't necessary), then go with Advanced SystemCare Pro.

You may have lot of junk left from old install.

Try deleting the windows.old file and defragmenting your HDD with jkdefrag. Should help. With that hardware your system should be much faster than with vista. If that doesn't work, do a clean install of windows, booting from the dvd and reformatting your hard drive before installing. Any drivers that don't come with the windows disk can be obtained on the 1st update. Good luck

I suggest:
Install boostspeed trial (from auslogics.com) and see what it finds. It's a suite of utilities whose value far exceeds the cost (at least it has for me), but it will help troubleshoot your PC for less than a penny and no I do not work for them, I was using a different suite for a long time, and this one surpassed it.
TuneUp utilities is another one if you somehow hate boostspeed, I'd try next.
There is always Sandra, but that one is info overkill and not recommending to a novice.

You likely have a mess, but it might be salvageable, I wipe and drop when the going gets ugly (mainly as a time saver, but I backup my critical stuff, frequently to a USB pen drive that I know if my house catches fire, it's the one thing PC wise I need to run out with) but in order to make it easier, it helps to have C: only have your Windows on it, and the rest of what you use on other partitions, so only Windows OS is wiped out and maybe some other stuff that refused to install anywhere but in with the OS.

In my case I went from XP, so I had to do a fresh wipe and drop, and I discovered that Win7 had quite a few unnecessary services running by default that had me ripping my hair out for a little while, I typed in a .txt file all my details and put that on my USB pen drive, I have a 16 gig pen drive, runs about $40, and that's the escape hatch for me.

Tell me I'm crazy, it's OK, it won't be the first time nor the last.