4.01 M33-2 Won't hard boot all the way

My PSP Slim is 4.01 M33-2. Every time I try to hard boot my PSP Slim (as in turn it off all the way and then turn it back on), it will show the XMB's wavy background, show the disc loading icon in the bottom right and then do nothing else. It will not auto-boot into the UMD or open the XMD. I can open the VSH menu if I have it enabled, but that's all I can do.
The only remedy I've found is reseting flash1. That lets me get into the XMB (and resets all of my settings), but even if I change ABSOLUTELY NOTHING, once I shut down my PSP and try to hard boot it again, it will give me the same problem every time.
If I reset flash1 and get into the XMB, then put the PSP into sleep mode, then turn it back on, it will start up just fine. Only hard booting gives me the problem.
What's happening that's giving me this problem???

Any custom themes?

If so, reformat flash0 then flash1 and try again

Wally

Well, my memory stick has custom themes, but when I reformat the flash1 it resets the XMB so that the custom themes are no longer installed. I've also tried reformatting flash1 with no memory stick or UMD but I get the same problem as always.
Also, there's an option to reformat flash1 but no option to reformat flash0 so I don't know how I'm supposed to do that.
Buuut, you mentioned themes, so I went to themes and changed my theme to "Tasty Treat", and changing the theme fixed everything as far as I can tell! So, thanks!