Need help with screwed up laptop

Not sure what is going on with my Dell laptop. I'm constantly missing files that should be there. I can't even find my C drive anymore! I've worked with this laptop for 4 years and never had these problems. I've worked with other laptops for years and never experienced this. Some things still work great, but I am spending the majority of my time trying to figure out what's going on with my laptop instead of being able to work on it! The warranty just ended, of course! I depend on this laptop for my living, so I can't afford to send it away for 2 weeks while someone looks at it and tries to fix it. I need to go somewhere or have someone come to me who is a real expert on fixing PC problems as well as software problems. I can't afford a new laptop for another year. But if I could have someone spend a few hours with me to help me figure out what's what, that would be great. I don't know if it's cost prohibitive or not, but I sure would like to try. I don't want someone just to sit down and tell me I need to buy a new one, nor do I want someone to tell me I just need a factory reset. I did that 6 months ago when it was still under warranty. Or if someone does tell me that, I want an expert who knows why. I need an expert who knows what they are doing so they can show me what I'm doing wrong, or what happened that it got this way. Bottom line, I do want it fixed, but there are so many little quirky things going on, that I need a repairman who not only knows how to fix computers and software problems but who also doesn't mind sitting with me for a bit. I want to try to point out all of the oddities and hopefully have someone show me how to fix them. I'm a quick learner and used to be pretty good at repairing my other laptops after I got to know them a bit. I would think it was harder back then than it would be now, but who knows? I don't think it's malware or a virus, because I do have malware and anti-virus protection. I realize that doesn't guarantee nothing will get through, but I'm very careful with what I do and what I download. I try to read everything before I download it, and I never go to a site that isn't VERY reputable to do so. Still, I know it happens. But if that's the case, why are some parts still working so well? Anyway, I am in need of 2 or 3 hours of in-person help. Is there anyone who does that??? Please let me know. Thank you!