Hello. I have a ten year old Lenovo Thinkpad W500 running Windows 7 Home Premium SP1 64-bit with 4 GB RAM.
HDD: 95 GB free out of 148 GB

It is currently having a problem with overheating. Yesterday I noticed that my CPU and Motherboard were around 80 to 90 degrees Celsius after four hours of usage. Today I was using it and noticed that my CPU  and Motherboard were 80 to 90 degrees Celsius after one hour of light usage. Please help! I used to be able toto use it longer than four hours and the temp be at 50 degrees Celsius just two days ago! I do have access to a WinXP laptop but it needs a new battery to boot up. And I have access to four flash drives in case I need to put a file on the computer.Hi

The first THING to check  is air flow out the left side of the laptop. If there is no air being blown out , can you hear the fan spinning? it will be at maximum speed with those temperatures. If the fan isn't spinning then it is likely faulty and will need to be replaced. A faulty fan is unlikely as without the fan the laptop would get to those temps in minutes not hours.

See here how to do this  https://support.lenovo.com/nz/en/solutions/migr-71370

If the fan is spinning but there isn't airflow then the HEAT sink fins maybe blocked with dust. You can often clear the blockage with a can of compressed air but you need to hold the fan to stop it spinning with the compressed air.

Last option is that the heat sinks need re mounting, this is unlikely and  not something a user should attempt.
    Ugh. Not good. The issue, that is.Ugh. I do not know how to open the laptop up and check, and if I use a guide I will probably misunderstand the guide and do it wrong. Can not afford a professional to do it. I am experienced with software and OSes, not with opening up computers. When I first start the laptop up and for a hour or so after, I hear air blowind but not after. Today, when I booted the laptop up, I heard no air blowing. Ugh. This is my main laptop, fan has probably been clogged with dust. How do I get into BIOS to turn the fan speed up to see if that works? Guide to open up the laptop to check the fan?The guide VintronNZ linked to above is very detailed regarding how to disassemble and reassemble your laptop.  If you aren't able to follow those instructions yourself and can't afford to pay someone to do it, maybe you have a friend that could do it?

That's the real fix, open the laptop and clean the dust and lint out of it but as a band-aid, you may be able to improve things by using one of those external laptop coolers that you place underneath the laptop that increase the airflow into the laptop thru the bottom.  They are really just a band-aid though.  Here's an example: https://www.amazon.com/gp/product/B01469DJLM?tag=laptop-magazine-20If the fan is clogged, it is probably clpggef with pet hair from my constantly shedding, yet loving, pets.What strollin suggested works ok with laptops that draw air thru the bottom of the laptop or if the chassis is made of a metal. This is not the case with your laptop so would have little benefit. If you just ignore this it is possible you will damage the video chip and then a simple cheap fix will become "almost not worth repairing".
A heat sink clean out  and fan check should take less than an hour tops for a technician to do and will save a lot of grief later.   Okay... good point. Definitely will get technician when I get my next paycheck.Okay. I admit it. I am sick and tired of this problem. I really need to work on a Wordpad document on this computer right now but can't because it "overheated " badly "sigh" again, and it is in sleep mode cooling off and I really need help with this problem. Please help!Chances are the heatsink is clogged up. There is no magic software or registry tweak or whatever you can install to fix it, and you've already been advised that you can either clean it yourself, or, if you do not trust your abilities, get somebody else to do it.

You may at least want to check the vents on the bottom of the laptop- this is where the W500 draws in air, and as a result it may be clogged up. You might be able to clear some of it and get at least get usable temperatures. Strollin's solution of a cooling pad might help a tiny bit- if nothing else it will improve the amount of air that can get through the ridiculously small intake vents. However it would be wiser to put that money towards having somebody qualified take a look at and clean out the heatsink of the system.

And as Vintron mentioned, continued use in this state will eventually result in the system effectively destroying itself and becoming completely unusable and more expensive to repair than to replace.
The problem is, I have to use the laptop regularly until the BEGINNING of next month, due to a project I have to do on it. Well, it looks like my budget will be tight due to taking it to a pro. Looks like I have to get the battery next month. I am using AC power.Yeah. Those are ridiculosly small. One of them is clogged, and another one is about a tenth clogged. Definetely going to use an external fan until I can afford a technician. Noticing the temps are around 60 - 70 degrees celcius now, not as desireable as I would want it to be, but a slight cool down in temps, thank goodness.I noticed the temps cooldown yesterday when I booted the computer up. Giving the computer a rest today.