techbrain1,
Thanks for sharing what details you have noticed instead of just one detail.
slow operations with my laptop: This part is vague, can be all sorts of things.
Slow response from applications and/or files: Again, can be a lot of things - is it EVERYTHING or just some programs and or types of files?
Freezes and have to reboot: Can be lots of things: Does it happen all the time, or just after certain actions? If all the time, is it usually after a particular event, or after some amount of time?
at times, the screen becomes dark but upon rebooting, the screen comes back: This one gives more insight, I think. Does the screen totally go blank in a second, or does it slowly darken over time? Either way, I think this may very well point to hardware issues. Chris stated it could be the CPU overheating, which I agree if the screen goes immediately black. However, if the screen is dimming slowly over time rather than instantaneous, the problem may be a power problem. Another source can be the graphics card/chipset or the LCD monitor itself. One easy test to narrow all this down if you have an external monitor, you can connect to that instead of your built-in laptop LCD, and see if the screen symptoms are the same.
If it turns out that it's a screen issue only, then you may have yet at least one other issue going on. For the freezing, requiring reboot, etc, it could also be:
1. Hard Drive going bad: which reminds me: Regardless of issue, if you have any important data, now would be a good time to backup whatever you can. If possible, remove the drive from your laptop, connect to another computer via an adapter or dock, and copy your files onto another drive.
2. Motherboard - Maybe? I don't think it's likely the culprit
3. Some major software issue: OS files majorly corrupted and/or virus/malware infection: One way to test whether software involved can be to reboot to Safe Mode (can use F8 on versions prior to Windows 8, and sometimes on some Windows 8/8.1/10 computers but not often) - If you can boot to safe mode, and the computer act half-normal, then it may be software. Could in theory still be the CPU overheating, but you should usually be able to get it to go whacky again even in safe mode if it's the CPU.
So my suggested actions at this point:
1. Remove hard drive, and back it up somewhere else. If that is not an option, boot from a Linux Live CD/DVD/USB Flash drive with whatever you want to use. Ubuntu has long been an easy one to work with. You can use the Linux OS then to backup the files - if you've never used Linux, it may take a little getting used to, but if you're tech-savvy you should be able to get by enough to get your files. And there are lots of online resources/instructions to help.
2. Once backed up, put drive back in laptop, if removed.
3. Next, try to boot to safe mode, if it loads ok, try doing whatever you want to try to see if you get the same issues.
3. Look and listen carefully to anything that seems out of the ordinary since the last you remember "ordinary" operation.
4. Report back with whatever you find.
5. If this is an older PC, consider whether you want to spend all this time anyway.
"But thanks be to God, which giveth us the victory through our Lord Jesus Christ." 1 Corinthians 15:57