Just an FYI – Avast released the fix with a new version 7.0.1456 that fixed many of the problems that users were having. In your case, I would suggest a clean install to see if it fixes you update problem.
Avast Free AV: http://files.avast.com/iavs5x/avast_free_antivirus_setup.exe
Avast Pro AV : http://files.avast.com/iavs5x/avast_pro_antivirus_setup.exe
Avast Internet Security: http://files.avast.com/iavs5x/avast_internet_security_setup.exe
I saw that another user posted in a thread: https://forum.avast.com/index.php?topic=100309.0 - see Post #8 that once he/she updated from SP2 to SP3 their problems with Avast went away. This may help you as well. It’s just an FYI. 
The way I understand the post,he\she didn’t even had a SP2(which I have)and he\she is not updating SP2 to SP3 but not SP\SP1 to SP2.
I’m currently using the newest update but it’s still in a testing period(one of the previous problems appeared again(the problems that came from 1451)but I’m not sure if the reason for if was avast again so I restarted the PC and I’ll see if some problem appear
I understand. If you are still having problems with Avast, you may want to consider getting v.1451 off you machine by uninstalling and doing a clean install, but make sure you reboot after the install. And I believe you already uninstalled all previous versions and products of Avast, but if you didn’t do this as well with a reboot in between while in Safe mode.
I removed 1451 by using the uninstaller and make a clean install of 1426 and today I updated by using the Update Program button to 1456
I didn’t have a single problem while I was using the clean install of 1426
I know you don’t want to hear it, but upgrading to SP3 might resolve your problem(s) since there are changes in the new version of Avast and many security upgrades in SP3. If you really don’t want to upgrade to SP3, since we’ve discussed this before, then you may be stuck with Avast v. 1426 (but now you would have to uninstall and do a clean install again).
Currently I don’t have any problems with 1456,I’m waiting to see if a problem appear.
The problem I mention above could be because of me(I was doing things that can cause a problem to appear),I’m not blaming avast for it yet.
Now your starting to sound like me. 
Keep on testing and let us know how it goes.
I guess this new update really fix the problem with 1451…almost 10 hours later,not a single problem.
Finally good news! 
I’m very happy for you.
If you want to continue testing, then go ahead. When you feel that your issue is resolved, then add “[RESOLVED]” in front of the title of your first post to close the thread.
Otherwise I will continue to assist you.
The problem is resolved but I’m trying to figure out why chrome should be installed without your approval.
It didn’t get installed here so I’m trying different thing to invoke this problem but still nothing.
There are many threads in the forum re: this issue. If you did a clean CUSTOM install, and unclicked the install Chrome boxes, it should not install. If you just clicked away without reading while you were installing, you most likely missed it and installed it. But you can still uninstall Chrome after installing Avast. I always suggest Custom installs and read before you click anything…yes, I’ve learned from my mistakes in the past. :-X
Yes I always use custom install on anything and remove what I don’t need.
It was long time ago when I was the “Next=>Next=>Next=>Finish” type user
I was thinking…could it be because of the UAC service…I’ve seen tons of problems because of it.Are there XP users with this chrome installing problems?
Yes, but again many are not doing the Custom install, or are upgrading from a regular install. I still think it may be something for Avast to look into, but considering the amount of users who have either upgraded or did a fresh install, the forum usually represents the users with problems, so you are talking very few users who didn’t have problems vs. the ones on the forum with problems.