For one thing, to be able to use the current object variable ($_) you need a pipeline context. Simply putting an if statement after echoing a variable doesn't automagically feed the echoed value(s) into the if statement. You need to change this:
$oldComputers if ($_.Name -notlike "1919DD" -or ...) { Export-Csv c:\temp\Over90DaysMachines.csv -NoTypeInformation -Force -Append }
into something like this:
$oldComputers | Where-Object { $_.Name -notlike "1919DD" -or ... } | Export-Csv c:\temp\Over90DaysMachines.csv -NoType -Force
However, even with that change your filter won't work correctly, because you connected the -notlike clauses via -or when you should have used -and. You obviously meant to process objects only if their name doesn't match any of the given values. But for your logical expression to evaluate to $false the name would have to match all of the reference value at the same time. Which clearly isn't possible, thus your expression always evaluates to $true.
Example:
Assume that you have a variable $v that should not be equal to either A, B, or C. Applying your logic, the expression would look somewhat like this in PowerShell:
($v -notlike 'A') -or ($v -notlike 'B') -or ($v -notlike 'C')
If $v takes for instance the value A that expression becomes
('A' -notlike 'A') -or ('A' -notlike 'B') -or ('A' -notlike 'C') ⇔ ($false) -or ($true) -or ($true) ⇔ $true
To check if a give value equals neither of the reference values you need to connect the clauses via -and:
('A' -notlike 'A') -and ('A' -notlike 'B') -and ('A' -notlike 'C') ⇔ ($false) -and ($true) -and ($true) ⇔ $false
$oldComputers | Where-Object { $_.Name -notlike "1919DD" -and $_.Name -notlike "1919SMAHESHWARE" -and $_.Name -notlike "1919IETEST" -and $_.Name -notlike "1920BPASCERITB" } | Export-Csv c:\temp\Over90DaysMachines.csv -NoType -Force
Note BTW, that the -notlike operator behaves exactly like the -ne operator when the reference string doesn't contain wildcard characters. If you're not doing fuzzy matches anyway you could simplify your expression by checking if the given name is (not) found in an array of names instead of doing multiple checks for (in)equality:
$excludes = '1919DD', '1919SMAHESHWARE', '1919IETEST', '1920BPASCERITB' $oldComputers | Where-Object { $excludes -notcontains $_.Name } | Export-Csv c:\temp\Over90DaysMachines.csv -NoType -Force
Another option would be a regular expression (non-)match:
$oldComputers | Where-Object { $_.Name -notmatch '^1919DD|1919SMAHESHWARE|1919IETEST|1920BPASCERITB$' } | Export-Csv c:\temp\Over90DaysMachines.csv -NoType -Force
