Vista - Internet connection lost

Hello, I run Vista Home Premium HP a6130n and I am having trouble with losing internet connection. Use to be worse but got updated modem from A T & T. Was 3-4 times a day, now 1 sometimes 2 times a day.
Doesn't happen when I am working, happens when I come back to the computer after being gone for a while.
A T & T says it's not them, it is my computer.
Event Viewer isn't helpful or I don't know what to look for. I am almost ready to go to the Geeks at Best Buy but wanted to give you people a shot.
I run the following programs for computer upkeep.
Advanced System Care 3
CCCleaner, cleaner and registry cleaner
Threatfire once a week
Easy Cleaner, Toni Arts
Malwarebytes Anti-Malware
Spybot Search and Destroy
AVG Free run every nite
and have found no significant problems
Have all the Windows updates
Have had A T & T for about 3 years and the problem is ongoing since then.

The new problem is having trouble with restart. Going to Start and then using the restart from there, hangs until I have to turn off the tower, yeah I know bad thing. This is recent, maybe the last two weeks. Sometimes works, sometimes doesn't. Downloaded Google Desktop and they wanted to restart the computer and there was no problem with that.
All help appreciated and if you need more info, pls let me know.
TIA,
Brenda

After a week of repeated network drops, I found the following from MS:
" Vista 64 and routers
To resolve this issue, disable the DHCP BROADCAST flag in Windows Vista. To do this, follow these steps: Click Start, type regedit.
If you are prompted for an administrator password or for confirmation, type your password, or click Continue. Locate and then click the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{GUID} [this is the first numeric string startins with {90...
Right click on DhcpConnEnableBcastFlag, Modify, and set the value to 0 (numeric zero). I then rebooted.
I have not had a drop in 24 hours. Hope it continues. Found this at: support.microsoft.com/kb/928233 "This issue occurs because of a difference in design between Windows Vista and Microsoft Windows XP Service Pack 2 (SP2). Specifically, in Windows XP SP2, the BROADCAST flag in DHCP discovery packets is set to 0 (disabled). In Windows Vista, the BROADCAST flag in DHCP discovery packets is not disabled. Therefore, some routers and some non-Microsoft DHCP servers cannot process the DHCP discovery packets."

OOPS... Did have one drop after the computer 'woke' up from a long winter's nap...several hours. The connection dropped. That might be yet another Vista issue -

"VISTA Sleep and Domain Network Drop Out problems". I am told there will be a fix in a coming service pack. The mouse is affected also. Fix or work around. We'll see...