Is my computer dying (Inspiron laptop)?

I have a Dell Inspiron 1750 laptop with 4 GB of RAM, a 500 GB hard drive, and a Intel Core 2 Duo T6600. It came with Windows 7 Home Premium 64-bit, but I downgraded to Windows Vista Home Premium 32-bit (with a disc that came with my Dell XPS, but that's beside the point). After noticing a drop in performance, I installed Windows 7 Ultimate 64-bit. I have ran this OS before, it worked flawlessly. Until now. Boot up time is very noticeably longer, and I can only run 1 or 2 programs at once without it crashing or locking up (I used to be able to run 10+). I can't CTRL + ALT + DEL or I get a black screen and an error. I can't shut down though the start menu or my computer locks up (either way, I need to do a force shut down). I get memory dumps constantly. I decided to re-install Windows Vista again, and I have the same problems. I've re-installed both Vista and 7 many times and the problems are not resolved, so it can't be the OS or programs. I have gotten the task manager to open a few times, and under the monitor, the CPU/RAM is barely being used. I'm worried that it may be dying. It's no longer under warranty, so I can't send it in for repairs.