Windows fails/very slow to start?

I've been having some problems with my computer. Its an HP Pavilion d5100t. Running Windows 7 Home Premium 64-bit. Within the last week or so, whenever I boot it up, Windows either takes a very long time (10+ minutes) to start, or doesn't start at all. Or at least the signal to the monitor shuts off during startup. The little green LED next to the power button on the CPU tower that signifies the computer is "thinking" sometimes continues to come on after the monitor loses signal, but obviously I can't see whether the computer is actually doing anything or not. There is a screen with the HP logo that appears immediately after turning the power on and it seems to stay there a lot longer than it used to. Then it goes to a black screen and a little flashing text cursor pops up in the top left corner of the screen. It used to breeze past this screen in a matter of seconds, but this seems to be where it is really hanging up. It will spend several minutes on this screen with the flashing cursor; then when the monitor signal fails it is usually at that point, or it will continue booting, but still go much slower than it should. My initial thought was that it was some sort of virus/malware or a system file had become corrupted. It had been a long time since I had done a clean format and I had already kind of been thinking about doing that anyway just to get rid of the junk that naturally builds up over time. So I went ahead and after making sure the important stuff was backed up, I ran the built in HP system recovery application, which wipes the C: and does a clean Windows installation from the recovery partition. But that didn't seem to help at all. So now I'm thinking its a hardware issue of some sort. btw... Once Windows actually starts there are no apparent problems. It runs just as I'd expect a clean computer with a fresh Windows installation to run. It just takes forever and sometimes multiple attempts to get there. Anybody experienced this before or have any ideas of what could be causing it? Probably going to take it in to my computer guy next week, but it would be nice to have some idea of what I'm looking at beforehand.