My laptop is getting slower and slower, help please!

Hi, I have a laptop 'Acer Aspire 5820T Timelinex' and I bought it back in 2010 in Italy. Today I own 3 more laptops but 5820T is special for me! I want to keep it forever, I tried to maintain its OS and it's pretty clean software wise. The thing is, it is getting very very slow, and yesterday, after 7 years, I disassembled my laptop and I found out that it had too much dust, I cleaned the 95% of it but it is still very very slow and I am pretty sure that it is hardware problem, so any help would be great and if my laptop needed new parts, I would be happy to replace.

P.S. an hour ago, laptop over heated quite a lot