My Computer Is Way Too Slow

My computer has gotten so slow lately, it's driving me crazy. I'm pretty sure I got it back in either 2003 or 2004. I'm not great at deleting old files, it's tedious and really hard for me to focus on it, so my laptop is close to full and I keep getting "you have no more room on your C: drive" messages. So I delete some stuff until the message goes away, and I'm usually good for another month or two.

But this time it's not JUST the warning message, the performance of the computer is really suffering. I'm having a hard time switching between applications. When I click on an application from the boxes along the bottom bar of my screen, instead of opening the program, the box just blinks orange. I've got to click it several times before the program comes to the forefront.

And it's taking me forever to download photos off my SD card. I don't know whether I messed up the SD card so it is difficult to read, or if the problem is with my computer. Or both.

Regardless, it's becoming downright frustrating to use. I scanned for viruses today to see if maybe that was the problem, but my computer is clean. I did fix some registry errors and emptied the recycle bin (well, as best I could, I kept getting error messages there, also). I've gotta figure out what's wrong and fix it. Until then, it's not a lot of fun using the computer, so I might not post as often as I have been.