Windows 7 Home Premium x64 speed problems?

Lots of details… Bear with me.

I'm not exactly a novice here but I can't figure this out. My computer (in the last 4-6 months) has been having some serious speed issues. It's a Dell Inspiron 531 with 4 gig of ram, an AMD Athlon 64 X2 Dual Core Processor 4400+ 2.31 GHz processor and an Nvidia GeForce GTS 250 graphics card.

It used to run amazingly fast. Now it isn't. I've run Glary, CCleaner and Malwarebytes. I've cleaned the junk files, defragmented the drive, registry and the memory. I have done everything I can for the beast and it's still bogged down. Here are the symptoms:

Excessive launch time for applications on first run. When I first launch Chrome or Firefox it takes upwards of a minute for them to open but the next time I run them they launch more quickly. Ssame problem with other applications.

Excessive time for save or open dialog boxes to appear. Often 30 seconds sometimes a minute or LONGER for a save dialog to appear (the first time.) After that the dialog opens fairly quickly.

Minecraft is running rather poorly as well. I used to be able to play minecraft with high quality graphics, shading, etc. Now I have jumpy graphics and lag even with low quality settings across the board.

It strikes me as a memory problem but I've run memory checks and they come back fine.

Also, with the above time issues. If I go an hour or so without opening a save dialog or launching a particular application then it will, again, take a long time to launch.

Any ideas?

Run burn in test and send me the log, also send, me the log of event viewer and I can see what's going on

Restore the computer to earlier date.