I have about an 8 month old hdtv, it's a vizio m320sl and I'm having 2 issues. I'm using it as a monitor for my pc andit is rated at 120hz refresh rate, however in the settings I see it can only go 60hz. Also it seems to be a bit laggy sometimes, for instance (and really the only time I ever notice) when I turn my pc on it lags. Like I won't be able to see the bios flash thing, and I miss it even loading windows sometimes. I'll turn my pc on (and the tv already being on) and it will take long enough where I only see the last bit or so of the loading windows screen (I do have an SSD so it isn't like a 1 minute delay). It never did this with my xbox.
for reference I'm using hdmi cable if that matters.
This is just a guess but until the video driver loads the HDMI output may not be active so you are not getting any video til then. This wouldn't be described as a 'lag' issue.
As to the refresh rate the TV is described as having a "120hz effective refresh rate".
That may mean that they use some processing to be able to say 120hz but not actually be able to do it.
120hz televisions display at 120hz but only accept a 60hz input signal. there lies your problem.
when the monitor processes (fakes) in the extra frames you can notice a delay when using it as a pc screen.
does your tv have a 60hz mode, game mode or pc mode? ultimately this is what you want (60hz display rate).
perhaps your tv automatically detects this and stutters a few times while your pc display drivers are being loaded. the order which you turn on devices can also matter. for instance if i turn the pc on and then my tv/receiver i will not have a display until windows loads. this is a result of autodetect i am betting. if i have the tv on first though i see bios, raid and winload.