Major Problems, please help

I have been having problems with my Inspiron 5150 since a few months after I got it.  It all began with my network connection.  Every now and then when I booted up the computer if it took a fair amount of time to load up, about 2-3 min. the internet (my LAN here at school) would not work.  This would occur about 1 in every 3 start ups.  Soon the problem became worse and it occurred in about 4 in every 5 start ups.  I didn't mind this too much until my computer started to shut down randomly.  Therefore causing me to start it back up 4 - 5 times to get the internet working again, only to have it shut down a little while later.  It seemed to shut itself down when the fan was on high which lead me to believe it was turning off to prevent over heating.  Virus checking and computer games caused the fan to run on high and there for shut down the computer.  I'd run the diagnostics disk many times and every test passes no matter how many times I test, nor what type of tests I run.  For one reason or another the DVD player on my laptop also didn't work (if I remember correctly) but it would however run CDs.  I soon became fed up with the machine and decided I might as well just reformat the hard drive and reinstall XP professional.  I deleted all partitions and began installing XP.  While installing XP the fan began running on high and surprise surprise, presto!  off went my laptop.  I was convinced that it was a hardware problem.  I turned my computer back on multiple times and it began installing XP again, at about the same point though the computers fan went on high and it turned itself off again.  Whether it be luck or cruel fate, the time I called dell and had a dell support women on the phone with me for 45 min. the thing installed correctly.  With very little on the computer I could do little to show her that the machine was still actually broken and that the flook start up was just fate laughing at me.  After reinstalling a few things and having the computer shut down on me a few more times, I called them back again.  This time a lady told me to upgrade my bios.  I was running version A01 and am now running a much higher version (I rather not restart and check, you'll understand why in a min.)  This finally fixed my problem.  The only small side effect was that now my power light didn't turn on except while the battery was charging (no biggie).  Soon I began getting an IRQL not less than or equal too blue screen error caused by bcwl (or something like that).  After calling dell up many times for that, with little help I researched IRQL errors and found that it was my wireless LAN card which was messing up.  So I reinstalled the drivers for that and made sure they were digitally signed.  Occasionally they go bad and cause a very slow start up and cause me to not have wireless signal when I am supposed to, so I simply reinstall them about every other week.  I'm currently on wireless connection 8.  (Goes up one each time I reinstall).  I've had problems with my wireless mouse and problems with my printer being detected but have both of those problems fixed at the time.  Now I have yet another problem.  (Oh yea by the way the computer is less than a year old).  Yesterday while trying to watch pulp fiction DVD on my laptop the movie stopped while playing in WinDVD 4.  I tried playing it in WMP but it didn't work same with real player.  I decided the best thing to do was, as always, restart and try again.  When I restarted the computer went on for approximately 7-10 seconds.  During this time the screen was black and the computer made no noise.  The scroll lock and the Caps lock buttons were illuminated but were not blinking.  After the 10 seconds the computer simply turned off.  I tried about 10-20 more times to turn the computer on to find the same thing happening over and over again.  I was delighted, since I knew that dell would have to take my computer back to the factory and fix it for real this time.  To my surprise the computer started up perfectly fine the next morning.  When I shut it down later that day and tried to turn it back on right afterwards the problem continued.  It seems that I have to give the computer about an hour to rest each time I turn it off or else it may not start back up again.  This has become a major problem while installing programs that require me to restart after installation.   I have yet to call Dell since most conversations with them take hours and resolve nothing, I have ran the diagnostics disk twice for all non-interactive tests and it passes.  I ran anti-virus software and found nothing.  Please help, what is wrong with my machine?  I need it for school.  I also want to add that I am not a computer guru but I am also not a dummy.  I don't know much about hardware but I know my software.  I would please please please appreciate any advice that you would have to offer.  I'm going to include all the specs I can think of at the bottom of this post.  Sorry for the length but I thought I should include all problems and details.   Dell Inspiron 5150  3.06 Ghz Processor  512 megs ram  40 gig hd   PS  I don't know if this has anything to do with my problem, or if it's normal or not by my bulky power supply chirps like a cricket when the computer fan runs on high.  Just thought I'd throw that out there.   Please respond