PC with slow boot and pc speed, sudden high pc usage, delay-freeze when opening/performing something

Question

Hi,
Before everything, two things:
1. I'm not a native english speaker so i may have some problems to speak properly/as objective as i'd like to.
2 . I'm writing in this section because i don't know the cause of my pc issues so i can't categorize them.
Now, my computer is a Toshiba satellite L755-S5244, Windows 7 Home premium 64 bits, Intel pentium CPU B940 2Ghz, 4 Gb RAM, and I'm writing this message using it.
I bought the laptop in December of 2011 and at the beggining it was working normally. Someone else used the computer these last months and he left the pc without antivirus protection; when i installed one (Avast) and start to analyze the pc it suddenly shutted down. It wasn't able to boot, so after some trys to restore/enter in safe mode I finally used the Toshiba Recovery Wizard to get the pc to the original factory settings. The process was sucessfull, so the first thing i did after finish the process was install a new antivirus (this time i used Kaspersky Pure) and the the analysis showed no threats as i expected.
However, before the recovery process i realized of some slow performance on the computer, like talking a bit too long to opening files or menus, control panel... almost anything was opening with a little delay even just after start the pc. This problem continued even after the recovery process. Also, an online game -League of legends- which was working fine when i just bought the pc, developed some issue: the screen and the audio randomly frezees for like 3-5 seconds. These problems seems to be related between each other.
But that wasn't all. After the recovery to the original factory settings, i just installed a few things:
-Kaspersky Pure 2.0, CCleaner (free), Mozila Firefox, and League of legends.
Later I also installed Microsoft Office 2010.
The antivirus showed no threats. The game kept with the freeze thing.
And 2 days ago i was playing league of legends and downloading Skype when the pc suddenly got too slow. I restarted it. After the restart it took a long time to boot, and before the windows login screen loaded there was a black screen where only the mouse was showed; the start-up was slow too, (this one showed a blue screen with the mouse too -but not BSOD-) all this took like 15-20 minutes; that never happened before so i restarted the computer again but the problem was the same: slow boot, slow desktop start-up (let's not even talk about opening something).
I went to the repair menu (f8) and try to restore the system but it didn't change anything. I checked for memory issues but there wasn't. I looked also for starting problems but the repair didn't find anything. All in there was saying: "the computer performance seems normal", but it wasn't. Like entering to windows in normal mode was talking to long, i tried the safe mode. It was also slow but not that much. When i entered, a system restore which i wasn't able to performance before in normal mode popped-up and said that the system was restored sucessfully to the first restore point -just after the factory recovery, but it apparently didn't fix the slow bot issue.
Even in safe mode the software was working slow so i decided to go for the toshiba recovery wizard again, and looked in here, the forums -and the rest of the net- for problems like mine.
This time the Toshiba Recovery Wizard took like ages to finish. 3 hours just for recovering, and like 7 more hours just installing the drivers. The boot/start-up was still slow, so i think this was the cause of the slow recovery because the wizard restarts the computer a lot.
When the factory settings recovery finished, the first boot was slow, also the start up, the programs, the start menu, the control panel, ... everything was slow the first time i opened it. If i keep using the same program, it seems normal, but randomly freezes if i select some option, of press something (like this browser, google chrome, even now when i'm writing this message or before where i was registering into the forums). As obvious, because this slow performance i'm really not comfortable using this computer.
I used the HDD SDD Alert but it says the HDD is working fine (the hard drive doesn't make weirds sounds, i almost don't hear it at all); also i did a PC Diagnostic with the PC diagnostic tool and everything passed the test. I can't think of virus/malware because i did the recovery wizard, twice. I just installed Avast again and it didn't find anything. With the task manager i noticed of a high pc usage (almost always 100%) was showing for a really short moment when/after the computer freezes.
So, i don't know how to solve this slow performance.
The last thing i did was download those speed-up softwares: SpeedUpMyPc, RegCurePro, SpeedyPC pro and Pareto logic Health Advisor. They scanned the pc for free and found like 100 system performance issues, but I'm not able to use these programms to fix the issues if i dont buy them. Also i'm not even sure if that will fix my problems.
That's why i'm here, looking for a way to identify/fix them. One last thing: all this time i've been checking the temperature of the laptop but is never hot -now is not even warm. Now i'm afraid of restarting the PC again cuz i know it will take a long time to get into a kinda stable performance like right now.
So that's all.  If you read all this, have my thanks. Also, any help would be really appreciated it.
EDIT: 
A new thing happened. When i try to installed league of legends, the setup told me that my hard drive may be corrupted and the file won't copy, i skip it a few times but the installation took a long of time (half hour) and the error kept ocurring.  I hope this can may be a clue about what is happening to my pc. 

Answer 1

Satellite L755-S5244
If you restore the hard disk to its original out-of-the-box contents using Toshiba recovery media and still have trouble, then you know it's not due to software.
the setup told me that my hard drive may be corrupted and the file won't copy, i skip it a few times but the installation took a long of time (half hour) and the error kept ocurring.
In particular, that sort of thing occurs when a hard drive is failing. Time to call Toshiba's tech support at 1-800-457-7777 (from the US) or 1-949-859-4273 (from outside the US).
-Jerry