Computer infected; believe it's malware; won't let me run AdAware or Malwarebyte

[SandlinComp]

I'm a new user to this site and need to see if anyone can give me some tips.  About two days, I noticed my browser has been hijacked.  When I search the normal Yahoo search bar, it takes me to a page that looks like it's should be right, but some of the links take me to various places I don't want to go.  My system is also locking up, it won't allow me to go back to a prior restore point, and no one can seem to help.  I have BSAFE online filtering with what I believe is McAfee.  I ran the scan and it's not picking anything up.  I also installed windows live care, and it didn't find anything either (so I removed it). 

I called Best Buy and they want to charge me 200.00 to attempt to fix.  But my computer is an older Compaq Presario and I can get one built for 350.00 that's 10 times better.  But I really don't have the extra cash and I am thinking about just wiping out the hard drive and doing a system restore with the original disks. 

That being said, any ideas?  Like I said in my subject line, I installed malwarebytes, and the inon is on my desk.  But when I try to run it, it won't do anything.  And it won't even let me start Ad aware.  So whatever is on my computer, it's taken control and won't allow me to do the things it knows will wipe it out.  HELP!!!!

[Geek-9pm]

$200.00 

Wow, for that plaice you can go get another computer.
If you have another computer, you can use it to scan the infected disk drive. You remove the hard drive from the infected computer and place it in the good computer as a slave. Do NOT run and programs  off the infected drive, don't even look at pictures on it. Use a good program, like megabytes, to do a full scan of the infected slave drive.
The vest way to 'slave' a standard HDD is to just place it on the cable used by the CD-ROM drive. Leave the CD-Drive off for now.  This is when the drives are the standard IDE type found on most computers made in the paste few years.
Some new ones are SATA and you would put a that drive on the second SATA plug in the good system.

In either case, check the BIOS to see if slave drive is found by the BIOS.
Now about the $200 thing. I think you would be better off investing in a good used computer just to have a backup system and to help you with future issues. I know that sounds like overkill, and a few years ago it was, but now used computers are even cheaper that a new HDD! Of course, they do not have all the power and storage you might want, but they have enough to serve ans a backup system.

Of course, you have to be careful about who you buy from. On eBay you can find out how long they have been in business and what kind of reviews that have received.