Windows 7 freezes for short spells (1 - 2 mins)

Hi
Windows 7 Ultimate SP1 all latest updates on 3MB R60 Duo 1.87Mhz. Full spec visible here http://speccy.piriform.com/results/D...gjG3baBceaALJ6

Runs fine most of the time but then occassionally (2 - 3 times per day) freezes for 1 - 2 minutes with the HDD light permanently on

One occasion just happened for c 40 seconds - fairly full machine and asked it to open an email with pictures in web browser (chrome). Nothing moved. Resource monitor froze. Task manager froze so it is difficult to report what was happening!!


Disk light on full time.
Resource Monitor shows
- Physical Memory around 80%
-average CPU 10% - 30%
- but very high (100/sec) 'page faults' and 'system' reading/writing furiously so I presume it isswopping files to and from HDD.
OK but why does it take so long? The PC can be locked up like this for 30 - 60 secs and it can write the whole of memory several times in 30 seconds.

There seem to be two different situations:
One (rare) where the entire PC locks up (not even the internal mouse nor tab key works) for a minute or so
The other where it becomes very slow (Ctrl-Alt-Del takes may be 45 sec to bring up task manager)
One of these just happened
'System' was writing at 1.2MB/s
svchost (netsvcs) reading 3.1MB/;s
Memory used was 2.6MB (3MB max)
and when that slowed down a bit 'trustedinstaller.exe started up and hogged one of the CPU for a couple of minutes doing what I have no idea

I've always been slightly concerned because in normal use when things are running OK, task manager shows kernel CPU as,typically, 50% of total CPU and that seems very high? Taskinfo reports WMI Provider Host (wmiprvse.exe)as using c.38% kernel CPU (Actually there are three threads each of which has short spikes - 2 of the pike every 5 secs or so and the other less often

And it wasn't always like this. I have a disk image somewhere (about a year old) which worked fine. If I decide to go back (and therefore redo several 00 windows updates) what can I do to help pinpont the problem - and no, one windows update at a time is not practical!!)

Things I've done
I've checked memory - no problem
I've checked the disk (HDsentinel) - no problem
I've chekdisk - no problem
I've run antivirus - no problems identified.
I've cleaned the disk
But as its intermittent I don't think is that sort of problem (clutter/virus/bad sectors)

Thanks but I did that as a matter of course. My fault should have said so