Evil Welcome Screen won't change

Here is my problem: I have an e-machine with windows xp, I have had it for over two years. I have never had any severe problems.
I haven't tried to do like a system restore or recovery or anything involving a disk (to be honest I lost mine, never had to use it). But I have tried everything else I possibly can think of. I get to my computer one day, and I noticed that the time was wrong, it said 7:30 a.m. when it was actaully like 3:52 P.M. I could not click on icons, and if I moved my mouse down to the task bar with the start button the mouse would turn into a hourglass, ctrl+alt+delete didn't bring up the task menu either.
I did the only thing I could think of and had to hold the power button for a manual shut down. When I tried to turn it back on, everythings seemed ok. then it got to the window screen saying it was loading preferences and everthing. then when the word "Welcome" came on the screen... it seemed like the computer stopped thinking. the light (don't know what it is called) that turns on when it seems to be processing things might barely turn on for like half a second, but nothing big happened after that. It stayed on that Welcome screen for over two hours. I could move my mouse around still, but no key process was recognized, ctrl+alt+delete did nothing and so forth.
So once again not being able to turn off my computer again, I did what I could think of, I did another hard shutdown. I repeated this process a few times trying to figure out how to get into the safety mode so I could work on it, but I didn't know the key for it, now I know it is F8, but I didn't know that, so I had to do a lot of manual shutdowns, anyway I first tried, last configure that worked (or whatever the option is) and that didn't help at all.
Then it developed a probem of now at the welcome menu, it would reboot after about 30 seconds, then repeat about 5-10 times before it got tired of rebooting, and just sat on the welcome screen some more. I finally figured out a not so good way of getting it to safe mode. I could enter it. But all is not well even there.
In safe mode, not all the progams work when I go into it. For example two times the add/remove program wouldn't work, another time I couldn't even open control panel. And every once in a while, the computer will decide to reboot itself with no promting and no warning. I even tried to do a computer system reset to a past date a month ago when I didn't have the problem, but apperantly that wasn't good enough. and it continues to torture me. By the way, it has been doing this for four days. I have even tried to wait out the welcome screen for more than 6 hours. I probably have done permanent damage with all of my manual shutdowns. But if anyone can help me, I am in desperate need. Thank you.

Could also try resetting your CMOS, directions should be in the manual. If you time is too badly messed up, Windows will not run. If you can into the BIOS after clearing the CMOS, reset the time. There are any number of other possible problems including a bad PSU.